The distribution profiles of very low density and low density lipoproteins in poorly-controlled male, type 2 (non-insulin-dependent) diabetic patients

Myeloperoxidase and paraoxonase-1 in type 2 diabetic patients

BACKGROUND AND AIMS

Reduced high density lipoproteins (HDL) and increased oxidative stress are features of type 2 diabetes. Myeloperoxidase is an oxidative enzyme partly associated with HDL and causing HDL dysfunction. It is an independent risk factor for cardiovascular disease. Paraoxonase-1 is an HDL-associated enzyme that protects against cardiovascular disease and is reduced in diabetes. The present study examined if serum myeloperoxidase was (i) increased in type 2 diabetes, (ii) correlated with paraoxonase-1 activity.

METHODS AND RESULTS

The study was based on cross-sectional analyses of serum myeloperoxidase and paraoxonase-1 in type 2 diabetic patients and non-diabetic participants, with and without cardiovascular disease. Serum myeloperoxidase concentrations were not increased in type 2 diabetic patients without cardiovascular disease compared to non-diabetic controls. They were significantly higher in type 2 patients and non-diabetic patients with angiographically confirmed coronary disease. HDL-associated myeloperoxidase was correlated with serum myeloperoxidase (r=0.80, p<0.001) but not HDL-cholesterol (r=0.08) or apolipoprotein AI (r=0.08). Multivariate analyses showed serum myeloperoxidase to be an independent determinant of paraoxonase activities (arylesterase, p=0.024; paraoxonase, p=0.026).

CONCLUSIONS

Myeloperoxidase is an independent, negative determinant of paraoxonase-1 activity, which may be one mechanism by which it promotes HDL dysfunction and increases cardiovascular risk. Increased serum myeloperoxidase is not a feature of type 2 diabetes in the absence of overt cardiovascular disease. The level of HDL-associated myeloperoxidase is determined by the serum concentration of the enzyme suggesting that, in the context of reduced HDL concentrations in diabetic patients, myeloperoxidase may have a greater impact on HDL function.

Paraoxonase-1 and serum concentrations of HDL-cholesterol and apoA-I

Paraoxonase-1 (PON1) and HDL are tightly associated in plasma, and this is generally assumed to reflect the need for the enzyme to associate with a hydrophobic complex. The association has been examined in coronary cases and age-matched controls. Highly significant (P < 0.0001), positive associations were observed between PON1 activities and concentrations and HDL-cholesterol and apolipoprotein A-I (apoA-I) concentrations in cases and controls. Corrected slopes were significantly different in cases (cases vs. controls: arylesterase, r = 0.19 vs. 0.38, P < 0.02 for apoA-I and r = 0.15 vs. 0.34, P < 0.02 for HDL-cholesterol) such that if PON1 should influence serum HDL, it would be less effective in coronary cases. When examined as a function of the PON1 gene promoter polymorphism C-107 T, highly significant differences (P < 0.001) in HDL-cholesterol and apoA-I were observed between genotypes for controls, with high expresser alleles having the highest HDL concentrations. This relationship was lost in cases with coronary disease. The coding region polymorphisms Q192R and L55M of the PON1 gene showed no association with HDL. The promoter polymorphism was an independent determinant of HDL concentrations in multivariate analyses. These data are consistent with an impact of PON1 on plasma concentrations of HDL, with detrimental modifications to the relationship in coronary cases.

Alterations of lipids and apolipoprotein CIII in very low density lipoprotein subspecies in type 2 diabetes

AIMS/HYPOTHESIS

Very low density lipoprotein (VLDL) particles are heterogeneous, comprising two main subspecies, VLDL 1 (Sf 60-400) and VLDL 2 (Sf 20-60). The aim of the study was to examine the distribution and composition of VLDL subspecies in type 2 diabetes.

SUBJECTS, MATERIALS AND METHODS

We studied the composition and concentration of triglyceride-rich lipoproteins (TRLs) in 217 type 2 diabetic patients and 93 control subjects between 50 and 75 years of age. Lipoprotein subspecies were separated by density-gradient ultracentrifugation. Apolipoprotein (apo) CIII and apo E in plasma and apo CIII in TRL subspecies were measured by nephelometry and apo CII in serum by a commercial kit using a single radial immunodiffusion method.

RESULTS

The concentrations of VLDL 1, VLDL 2 and intermediate density lipoprotein were significantly increased in type 2 diabetes subjects, the change being most marked for VLDL 1. There was a strong linear correlation between VLDL 1 triglycerides and plasma triglycerides in both groups (r = 0.879, p < 0.001 and r = 0.899, p < 0.001). Diabetic subjects had markedly higher plasma ratios of apo CII:apo CIII and apo CIII:apo E. Despite elevated plasma apo CIII, type 2 diabetic subjects had a relative deficiency of apo CIII in all TRL subspecies, suggesting profound disturbances of apo CIII metabolism.

CONCLUSIONS/INTERPRETATION

The elevation of VLDL 1 triglycerides is the major determinant of plasma triglyceride concentration in normal subjects and in type 2 diabetic individuals. Both apo CIII and apo E metabolism are disturbed in type 2 diabetes.

Effect of improving glycemic control on low-density lipoprotein particle size in type 2 diabetes

The current study sought to assess the effect of improving glycemic control in type 2 diabetes on the components of diabetic dyslipidemia, especially low-density lipoprotein (LDL) size. A total of 33 type 2 diabetic patients (48.5% women, age 59.6 +/- 11.1 years, body mass index [BMI] 28.9 +/- 4.9, diabetes duration 6 [0 to 40] years, 40.7% on insulin) were seen at the hospital because of poor glycemic control (hemoglobin A(1c) [HbA(1c)] 10.33% +/- 1.89%). Triglyceride, LDL-cholesterol (LDLc, Friedewald/ ultracentrifugation), high-density lipoprotein HDL-cholesterol (HDLc, direct method), apolipoproteins AI (apoAI) and B (apoB) (immunoturbidimetry), and LDL size (gradient gel electrophoresis) were measured at baseline and after improvement in glycemic control (decrease >/= 1 percentage point in HbA(1c) and final HbA(1c) </= 8%). Improvement in glycemic control (HbA(1c) 7.01% +/- 0.63%, P <.0005 v baseline) after a follow-up of 3.5 (range, 1 to 13) months resulted in a significant reduction in LDLc (3.34 +/- 1.02 v 3.62 +/- 1.15 mmol/L, P <.05) and apoB (1.07 +/- 0.25 v 1.17 +/- 0.29 g/L, P <.01) and an increase in HDLc (1.21 +/- 0.32 v 1.13 +/- 0.34 mmol/L, P <.05) and apoAI (1.36 +/- 0.24 v 1.27 +/- 0.24 mmol/L, P < 0.01) in the whole group, and an increase in LDL particle size (25.61 +/- 0.53 v 25.10 +/- 0.31 nm, P <.005) in the 14 patients showing LDL phenotype B at baseline. No significant changes were seen in body weight or BMI. We conclude that improvement of glycemic control in type 2 diabetes improves most of the components of diabetic dyslipidemia, including a shift towards larger LDL particles in subjects with phenotype B.

Low-density lipoprotein subclass and its correlating factors in diabetics

OBJECTIVES

Small dense LDL, low density lipoprotein (LDL) particles with small size and high density, is regarded as a significant risk factor for cardiovascular diseases. Diabetes mellitus is one of the conditions accompanied by increased small dense LDL. We analyzed LDL subclass in type 2 diabetics and normal controls with LipoPrint LDL System to investigate the LDL heterogeneity in diabetics and factors affecting it.

DESIGN AND METHODS

We selected 40 normal controls and 40 type 2 diabetics with fasting blood glucose level over 7.0 mmol/L and HbA1c level over 7%. LDL subclass was determined with LipoPrint LDL System. LipoPrint LDL System fractionates LDL into seven parts (LDL1-7) by size and LDL3 to LDL7 are defined as small-sized LDL. In addition we estimated 'the percent of small-sized LDL over whole LDL' and defined it as 'small-sized LDL proportion'.

RESULTS

Mean small-sized LDL proportion was significantly higher in diabetics (23.4%) than in controls (11.8%) (p<0.001) and small-sized LDL proportion showed positive correlation with blood levels of glucose, HbA1c, total cholesterol, triglyceride, and oxidized LDL and negative correlation with HDL cholesterol level in univariate analysis (p<0.001). Of these parameters, triglyceride, HbA1c, oxidized LDL were statistically significant variables contributing to the small-sized LDL proportion in stepwise multiple regression analysis.

CONCLUSIONS

We analyzed small-sized LDL proportion in type 2 diabetics and found that it was significantly increased in diabetics than control subjects and it was independently correlated with triglyceride, HbA1c, oxidized LDL in descending order, which are reflecting lipid metabolism, glycation, and oxidative stress, respectively.

Insulin treatment prevents LDL from accelerated oxidation in patients with diabetes

In a study population, we compared the level of malondialdehyde-modified LDL (MDA-LDL) with the concentrations of lipid parameters in serum and found a strong correlation between MDA-LDL and apolipoprotein B (apo B) concentrations. Their interrelations had a turning point at an apo B concentration of 1,150 mg/l. In diabetic patients, the ratio of MDA-LDL/apo B increased at apo B concentrations above 1,150 mg/l. This ratio represents the extent of modification of apo B by MDA. In the control subjects, this ratio remained stable. When we divided the patients into medication groups (statins and insulin), we found that the 1,150 mg/l threshold disappeared. At apo B concentrations above 1,150 mg/l, the ratio of MDA-LDL/apo B in the statin group was as high as that in the non-drug group. In the insulin group, the means of MDA-LDL/apo B in all ranges of apo B levels decreased to an extent statistically indistinguishable from those of the control group. In conclusion, insulin therapy represses LDL oxidation even at apo B concentrations > 1,150 mg/l and should be noted for its anti-oxidation properties.

The apolipoprotein epsilon2 allele and the severity of coronary artery disease in Type 2 diabetic patients

AIMS

To examine the hypothesis that apolipoprotein E2 is associated with more severe coronary disease in Type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

In this retrospective cohort study, 491 patients with angiographically assessed coronary disease were recruited from those attending a university hospital cardiology department. Participants completed detailed questionnaires, from which the presence or absence of diabetes was determined. Fasting blood samples were obtained for apolipoprotein E genotype and measurement of blood lipid parameters.

RESULTS

The prevalence of triple vessel disease was significantly lower in non-diabetic, epsilon2 allele carriers (39.3% vs. 16.2%; odds ratio (OR) 0.30 (0.12-0.71), P < 0.03) compared with E3/3 carriers. In Type 2 diabetic patients, epsilon2 allele carriers had an excess of triple vessel disease compared with E3/3 genotypes (43.3 vs. 68.8%; OR 2.8 (1.07-7.30), P < 0.05). The differences were independent of other variables. The apo E4 subgroup showed no significant differences in the frequency of triple vessel disease.

CONCLUSIONS

Diabetic epsilon2 allele carriers had more severe coronary artery disease than diabetic patients with other apo E isoforms. In non-diabetic patients the epsilon2 allele appeared to protect against severe coronary disease. We hypothesize that interaction between the diabetic milieu and the epsilon2 allele accelerates plaque progression. It suggests that diabetic patients who are carriers of the epsilon2 allele, even in the heterozygous form, should be the focus of particular therapeutic attention. Diabet. Med. 18, 445-450 (2001)

Serum paraoxonase is reduced in type 1 diabetic patients compared to non-diabetic, first degree relatives; influence on the ability of HDL to protect LDL from oxidation

Paraoxonase is a serum enzyme with an anti-oxidant function, protecting low density lipoproteins (LDL) from oxidative modifications. Diabetic patients are suggested to be at greater risk of oxidative stress, which may contribute to the significantly higher incidence of vascular disease in this population. Less efficient protection mechanisms may be one feature of the greater susceptibility to oxidation in diabetes. In this context, the present study examined the hypothesis that serum paraoxonase is reduced in type 1 (insulin-dependent) diabetic patients and that the reduction can affect the anti-oxidant capacity of HDL. Serum paraoxonase concentrations and activities were compared in type 1 patients and first degree, non-diabetic relatives with particular attention paid to the confounding effects of paraoxonase gene polymorphisms. In addition, the ability of HDL-paraoxonase to protect low density lipoproteins from oxidation was analysed in an in vitro system. Serum concentrations and enzyme activities of paraoxonase were significantly lower in type 1 patients compared to non-diabetic, first degree relatives. The differences were independent of promoter and coding region polymorphisms, which influence serum concentrations and activities of the enzyme. Overall, paraoxonase concentrations were a mean 13.3+/-4.5% lower (P<0.02) in type 1 patients. Specific activities did not differ between diabetic and non-diabetic groups. The concentration ratios of LDL cholesterol:paraoxonase (1.37+/-0.51 vs. 1.18+/-0.37, P=0.003) and apolipoprotein B:paraoxonase (0.84+/-0.33 vs. 0.71+/-0.40; P=0.012) were significantly higher in diabetic patients, consistent with a reduced capacity to protect LDL from oxidation. In vitro oxidation studies showed that a significantly higher level of lipid hydroperoxides was generated in LDL in the presence of HDL, containing paraoxonase levels equivalent to those of type 1 patients, compared to HDL containing paraoxonase levels equivalent to those of control subjects (mean difference 8.1%, P<0.05). The study demonstrates that serum concentrations of the antioxidant enzyme paraoxonase are significantly lower in type 1 (insulin-dependent) diabetic patients compared to non-diabetic, first-degree relatives, independently of known gene polymorphisms. Concentrations are reduced to an extent that can affect its anti-oxidant capacity. The results are consistent with the contention that modifications to serum paraoxonase in type 1 patients can increase risk of lipoprotein oxidation and, consequently, risk of vascular disease.

Smoking is associated with reduced serum paraoxonase activity and concentration in patients with coronary artery disease

BACKGROUND

Paraoxonase is an HDL-associated enzyme that protects lipoproteins from oxidative modifications. Smoking is a major cardiovascular risk factor that promotes lipid peroxidation. Cigarette smoke has been shown in vitro to inhibit paraoxonase. The present study examined the hypothesis that smoking is associated with modulated serum activities and concentrations of paraoxonase.

METHODS AND RESULTS

Coronary artery disease was assessed with the use of coronary arteriography in participants recruited from a hospital cardiology division. Medical and lifestyle data were obtained, and a fasting blood sample was provided. Three smoking categories were established (never, ex-smokers, and current smokers), and serum paraoxonase variables were compared among them. The activities and concentrations of paraoxonase were significantly lower in current than in never smokers. Ex-smokers had values comparable to those of never smokers. Ex-smokers who had recently stopped (<3 months) had activities and concentrations comparable to those of current smokers; values returned to the levels of never smokers within 2 years of cessation of smoking. Smoking status was an independent determinant of paraoxonase activity and concentration in multivariate analysis. Finally, lower paraoxonase was associated with more severe coronary disease and a reduced capacity to protect LDL from oxidation.

CONCLUSIONS

Smoking is independently associated with significant decreases in serum paraoxonase activities and concentrations, which normalize within a relatively short time of cessation. Lower serum paraoxonase is linked to more severe coronary artery disease and a lower antioxidant capacity. The data are consistent with the hypothesis that smoking modifies serum paraoxonase such that there is an increased risk of coronary artery disease due to a diminished capacity to protect lipoproteins from oxidative stress.

Acute hyperinsulinemia and very-low-density and low-density lipoprotein subfractions in obese subjects

BACKGROUND

The influence of hyperinsulinemia on concentrations of lipoprotein subfractions in obese, nondiabetic persons has not been clarified.

OBJECTIVE

We analyzed VLDL and LDL subfractions before and after a euglycemic, hyperinsulinemic clamp.

DESIGN

Lipoprotein subfractions were isolated from plasma samples obtained in the basal state and after a 4-h clamp from obese patients, obese patients with type 2 diabetes, and nonobese control subjects.

RESULTS

Hyperinsulinemia tended to reduce concentrations (&xmacr;: 20%) of large, triacylglycerol-rich VLDL(1) in obese patients but had a minor effect on VLDL(2) and VLDL(3). Placing obese patients into insulin-sensitive and insulin-resistant subgroups revealed distinct effects of the degree of insulin sensitivity on VLDL. VLDL(1) concentrations decreased by a mean of 38% (P < 0.05) in insulin-sensitive patients after the clamp, similar to but less marked than the decrease observed in control subjects (&xmacr;: 62%; P < 0.01). VLDL(1) concentrations did not change significantly after the clamp in insulin-resistant patients (and patients with type 2 diabetes), whereas VLDL(3) concentrations decreased in both groups, in contrast with the changes seen in the insulin-sensitive patients and control subjects. Acute hyperinsulinemia modified the LDL subfraction profile toward a greater prevalence of small, dense LDLs in insulin-resistant patients and patients with type 2 diabetes.

CONCLUSIONS

Insulin resistance appears to be the primary determinant of the modifications to VLDL subfraction concentrations. Our results suggest a continuum of impaired insulin action on VLDL, ranging from that in healthy persons to that in patients with type 2 diabetes, in which obese patients occupy a transition state. Insulin resistance may also play a role in detrimental modifications to the LDL profile by allowing the development of hypertriglyceridemia.

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.

The fatty acid distribution in low density lipoprotein in diabetes

Atherosclerosis is commonly found in diabetes. There is an association between small dense low density lipoprotein (LDL) phenotype, which is more prevalent in the diabetic state, and atherosclerosis. Small dense LDL is more easily oxidised and it is possible that fatty acid compositional changes, particularly an increase in polyunsaturated fatty acids, could underlie this association. However, there is little information about fatty acids in the different LDL phenotypes in the literature. This study examined LDL subfraction composition in 18 non-insulin-dependent diabetic (NIDDM) patients and 11 control subjects. LDL was isolated and fractionated into LDL 1, 2 and 3 by density gradient ultracentrifugation. NIDDM patients had significantly more fatty acids in all LDL subfractions than control subjects (P<0.01). Palmitic and linoleic acid were significantly greater in all subfractions in the diabetic patients compared to control subjects (P<0.01) and palmitoleic and oleic acids were also greater in LDL1 and LDL2 in diabetic patients (P<0.01). We conclude that in NIDDM fatty acids are increased in all LDL subfractions and this may be the reason for the increased atherosclerosis in diabetes irrespective of phenotype.

Lipoprotein atherogenicity: an overview of current mechanisms

Raised serum cholesterol does not adequately explain the increased risk of CHD within populations or the relationship between diet and CHD. Nevertheless, the principal transport vehicle of cholesterol in the circulation, LDL, must still be regarded as the most atherogenic lipoprotein species, but not because of its contribution to serum cholesterol. The atherogenic potential of LDL in the majority of individuals arises from an increase in the number of small dense LDL particles and not from its cholesterol content per se. There is now a wealth of evidence from cross-sectional and prospective studies to show that LDL particle size is significantly associated with CHD and predictive of increased coronary risk. Moreover, there are a number of credible mechanisms to link small dense LDL with the atherogenic process. The rate of influx of serum lipoproteins into the arterial wall is a function of particle size, and will thus be more rapid for small dense LDL. Components of the extracellular tissue matrix in the intima, most notably proteoglycans, selectively bind small dense LDL with high affinity, sequestering this lipoprotein in a pro-oxidative environment. The oxidation of LDL promotes the final deposition of cholesterol in the arterial wall, and numerous studies have shown small dense LDL to be more susceptible to oxidative modification than its larger and lighter counterparts. An increase in the number of small dense LDL particles may originate from a defect in the metabolism of triacylglycerol-rich lipoproteins. One mechanism may involve the overproduction and increased residence time of large triacylglycerol-rich VLDL in the postprandial phase, a situation thought to arise through pathways of insulin resistance.

Lipoprotein composition and serum apolipoproteins in normoglycaemic first-degree relatives of non-insulin dependent diabetic patients

Cardiovascular disease is the leading cause of death in non-insulin dependent diabetes mellitus and first degree relatives of such patients are at increased risk of developing diabetes and cardiovascular disease. The aim of the present study was to determine whether lipid abnormalities occur in normoglycaemic relatives of non-insulin dependent diabetic patients. Cholesterol, triglycerides, apolipoprotein A-I and apolipoprotein B concentrations were measured in serum; the lipoprotein fractions very low density, intermediate density, low density and high density lipoprotein were prepared by sequential flotation ultracentrifugation and their composition investigated. The groups were matched for age, sex and blood glucose concentrations although the relatives (n = 126) were more insulin resistant as determined using the homeostasis model assessment method [1.9 (0.8-9.0) vs 1.6 (0.4-4.9) mmol/mU per l (mean [95% confidence intervals]); p < 0.001] and had greater body mass indices [26.6 (4.1) vs 24.8 (3.9) (mean [S.D.]); p = 0.001] than control subjects (n = 126). Relatives had higher serum apolipoprotein B concentrations than control subjects [0.9 (0.3) vs 0.8 (0.3) g/l, p = 0.02) and lower serum apolipoprotein A-I concentrations (1.4 (0.3) vs 1.5 (0.3), p = 0.02). In multivariate linear regression analysis of all subjects log insulin resistance (p = 0.0001), age (p = 0.002) and waist:hip ratio (p = 0.01) were independent predicators of apolipoprotein B concentrations while waist:hip ratio (p < 0.001) and smoking status (p = 0.002) were independent predictors of apolipoprotein A-I concentrations. Lipoprotein composition (measured in a subgroup of 76 control subjects and 88 relatives), serum cholesterol and serum triglyceride concentrations did not differ between the groups. We conclude that atherogenic apolipoprotein abnormalities occur in normoglycaemic relatives of non-insulin dependent diabetic patients.

Modulated serum activities and concentrations of paraoxonase in high density lipoprotein deficiency states

Paraoxonase is a high density lipoprotein (HDL) associated enzyme with a hypothesised role in the protection of low density lipoproteins (LDL) from oxidative stress. The present study examined paraoxonase in several genetically distinct HDL deficiency states. Despite reduction or even absence of detectable HDL, enzyme activity was present in sera from A-I-Pisa, A-I-Helsinki, A-I-Milano and Tangier patients. Both enzyme activities and peptide concentrations were modulated (reduced) but specific activities were broadly similar to controls, suggesting an impact on peptide concentration rather than an inhibition of enzyme activity. Despite the absence of HDL in A-I-Pisa and Tangier subjects, there was no association of paraoxonase with very low density lipoproteins or LDL. Paraoxonase function is maintained in HDL deficient states. It implies that certain HDL-associated anti-atherogenic processes may not be entirely compromised by HDL deficiency. This has important implications for the cardiovascular risk associated with modulated HDL concentrations.

Apolipoprotein E polymorphism and the distribution profile of very low density lipoproteins; an influence of the E4 allele on large (Sf > 60) particles

Very low density lipoprotein (VLDL) distribution and composition have been examined as a function of apo E genotype (E2/2 + E2/3 vs. E3/3 vs. E3/4 + E4/4) in healthy, normolipaemic subjects. Apo E genotype had a marked impact on plasma concentrations of apo E rich VLDL, but no influence on concentrations of apo E free particles. Thus, there was a trend to lower concentrations of apo E rich total VLDL in apo E4 carriers (mg/dl; E2, 49.1 +/- 35.2; E3, 52.5 +/- 30.9; E4 35.2 +/- 22.3; ANOVA P = 0.16; when comparing E4 with E2 + E3, P = 0.06). Consequently, there were highly significant differences between apo E-defined subgroups in terms of the percentage distribution of bound and non-bound fractions (% total VLDL non-bound to apo E: E2, 44.0 +/- 12.7%; E3, 39.7 +/- 8.7%; E4 51.0 +/- 12.2%; ANOVA P = 0.007). Subfractionation of VLDL into density subclasses revealed that genotype differences were restricted to large VLDL (Sf > 60). Significantly lower concentrations of apo E-rich particles were observed in E4 carriers for VLDL-1 Sf 400-100 (ANOVA P = 0.004) and VLDL-2 (P = 0.009) but not for small VLDL-3 Sf 60-20 (P = 0.34). No differences in plasma concentrations of apo E free VLDL were observed between genotype subclasses across the density spectrum. Compositional differences between the apo E defined VLDL were also evident for the core lipids. Apo E containing VLDL was enriched in esterified cholesterol and depleted in triglycerides compared to apo E poor VLDL: the difference became more marked with increasing density of the particles. Lipoprotein composition was not modulated to any great extent by apo E genotype. In patients with familial hypercholesterolaemia, relative concentrations of apo E rich, large VLDL were significantly higher than in controls. Treatment lowered concentrations of both apo E rich and apo E free VLDL but led to a greater relative enrichment of large VLDL in apo E containing particles. Apo E polymorphism appears to influence plasma concentrations of VLDL particles. The data are consistent with more pronounced receptor-mediated elimination of apo E4 containing VLDL. This may be a contributory factor to the down regulation of receptor activity which is suggested to be of major importance in provoking higher cholesterol levels associated with the apo E4 isoform.

The effect of growth hormone replacement therapy for up to 12 months on lipoprotein composition and lipoprotein(a) in growth hormone-deficient adults

The effect of growth hormone replacement therapy in near physiological doses on lipoprotein composition and serum lipoprotein(a) concentrations was investigated in growth hormone-deficient subjects. A randomised, double-blind, placebo-controlled trial of recombinant growth hormone was undertaken for 6 months followed by an open extension for a further 6 months (0.125 IU/kg per week for the first 4 weeks of each 6 month period and thereafter 0.25 IU/kg per week). A total of 18 patients with isolated growth hormone deficiency or hypopituitarism were studied. Lipid concentrations were estimated in lipoprotein fractions and protein concentrations were measured in low density lipoprotein (LDL). Glucose and glycated haemoglobin in blood and insulin, cholesterol, triglyceride, apolipoproteins A-I and B and lipoprotein(a) concentrations were measured in serum. In the placebo-controlled phase fasting blood glucose concentrations increased with growth hormone treatment from 5.0 +/- 0.2 to 5.8 +/- 0.2 mmol/l (P = 0.02) (mean +/- S.E.M.), although no significant changes were seen in lipids or lipoproteins. In the group receiving active treatment total serum cholesterol decreased from 6.0 +/- 0.4 to 5.2 +/- 0.3 mmol/l (P = 0.002) after 6 months, due to reduced LDL cholesterol concentrations. Low density lipoprotein protein concentrations fell (0.8 +/- 0.1 versus 0.7 +/- 0.1 g/l) (P = 0.005), and LDL phospholipid levels decreased from 0.9 +/- 0.1 to 0.7 +/- 0.1 mmol/l (P = 0.007). Serum cholesterol and LDL composition reverted to pre-treatment values by 12 months. Fasting blood glucose remained above pre-treatment values (P = 0.036) and fasting insulin was significantly increased (P = 0.044). There was no effect of growth hormone therapy on serum triglyceride, apolipoprotein or lipoprotein(a) concentrations. In conclusion, growth hormone therapy with near physiological doses has no long term effects on serum lipoprotein(a) concentrations or lipoprotein composition.

Lipoprotein analyses in patients with stable angina and acute coronary syndrome

We have performed lipid analyses by using a table-top ultracentrifuge based on the Hatch and Lees' method in 77 subjects (60 men, 17 women: mean age, 63 years) to clarify lipoprotein disorders in coronary artery disease. Sixty-four subjects had coronary artery disease and 13 normal subjects were controls. They were divided into the groups with stable angina pectoris and with unstable angina pectoris or acute myocardial infarction (acute coronary syndromes). In patients with coronary artery disease, there were no significant differences from control in age, body mass index, total cholesterol, however, HDL cholesterol was significantly lower than those in the controls. LDL cholesterol:LDL apoB ratio, which is thought to reflect the size of LDL in coronary artery disease, was significantly smaller than that in the controls; mean values were 1.2 in coronary artery disease and 1.4 in controls. There were no significant differences in those lipoprotein disorders between the patients with stable angina and those with acute coronary syndromes. Though these lipoprotein abnormalities would not play a trigger role in acute coronary syndrome, they are characteristic of the lipid profile of patients with coronary artery disease.

Lipoproteins, apolipoproteins, and low-density lipoprotein size among diabetics in the Framingham offspring study

Diabetes mellitus has been shown to be associated with lipid abnormalities. Prior studies have indicated that women with diabetes have a risk of coronary heart disease similar to that of men. We compared lipid parameters in diabetic and nondiabetic participants in cycle 3 of the Framingham Offspring Study. Values for plasma total cholesterol (TC), triglyceride, lipoprotein, cholesterol, apolipoprotein (apo) A1, B, apo and lipoprotein(a) [Lp(a)] and low-density lipoprotein (LDL) particle size were analyzed in 174 diabetic and 3,757 nondiabetic subjects. Data from a total of 2,025 men and 2,042 women participating in the third examination (1983 to 1987) of the Framingham Offspring Study were subjected to statistical analysis. Male and female diabetics showed lower high-density lipoprotein (HDL) cholesterol, higher triglycerides, higher very-low-density lipoprotein (VLDL) cholesterol, lower apo A1, and higher LDL particle scores, indicating smaller size, than nondiabetics. Female diabetics also showed significantly higher TC and apo B values than nondiabetics. The results remained statistically significant after controlling for obesity and menopausal status. The presence of small dense LDL particles (pattern B) was highly associated with diabetes and hypertriglyceridemia in both sexes, and the relative odds for pattern B remained significant in women but not in men after adjustment for age and hypertriglyceridemia. No differences in apo E isoform distribution were found for diabetics and nondiabetics. Diabetes was not associated with elevated LDL cholesterol levels. In conclusion, diabetics have lower HDL cholesterol and higher triglyceride levels and are more likely to have small dense LDL particles. Diabetes is not a secondary cause of elevated LDL cholesterol. Lipid screening of diabetics should include full quantification of lipids for proper assessment of potential atherosclerotic risk.

New insights into lipid metabolism in non-insulin-dependent diabetes mellitus

Perturbations of lipid metabolism are common in diabetes. Therefore, an understanding of the underlying mechanism of lipid metabolism and in particular the role of insulin is a critical issue. The review aims to provide evidence that hypertriglyceridaemia is central to many features of diabetic dyslipidaemia.

Lipids and atherogenesis in diabetes mellitus

Premature cardiovascular disease is a major burden in diabetes. Increasing cholesterol is associated with increasing vascular risk in diabetes and the absolute excess risk attributable to cholesterol is higher in diabetes than in non-diabetics. Total cholesterol and low density lipoprotein (LDL) cholesterol correlated with arterial endothelial dysfunction as assessed by reduced flow-mediated brachial artery dilatation in insulin-dependent diabetic patients. In non-insulin dependent diabetic patients hypertriglyceridaemia is common and is associated with the accumulation of intermediate density lipoproteins, abnormal postprandial lipid metabolism and small dense LDL. No trials of lipid lowering therapy in the primary or secondary prevention of cardiovascular disease have been targeted specifically to the diabetic population; nevertheless, guidelines have been published for the treatment of dyslipidaemia in diabetic patients recognising the evidence of benefit in non-diabetics and the high intrinsic risk of the diabetic.

Abnormal cholesterol distribution among lipoprotein fractions in normolipidemic patients with mild NIDDM

This study was carried out to identify and define lipoprotein abnormalities in patients with noninsulin-dependent diabetes mellitus (NIDDM) who do not have clinical elevations of cholesterol or triglycerides. Thirty-four male patients with mild NIDDM and normolipidemia (plasma cholesterol < or = 240 mg/dl and triglycerides < or = 250 mg/dl) were compared with 35 healthy male normolipidemic subjects. The two groups had similar age and body mass index. Measurements in the two groups included concentrations and chemical composition of lipoproteins and sizing of low-density lipoprotein (LDL) particles. The patients with NIDDM, compared to control subjects, had two distinct lipoprotein abnormalities: first a significantly reduced level of high-density lipoprotein (HDL) cholesterol (mean +/- S.D., 35 +/- 8 mg/dl vs. 41 +/-10 mg/dl, respectively; P = 0.006), and second, a high cholesterol-to-apolipoprotein (apo) B ratio both in a very low density lipoprotein (VLDL) + intermediate density lipoprotein (IDL) fraction (mean +/- S.D.; 3.2 +/- 0.8 vs. 2.8 +/- 0.9, respectively; P = 0.02) and in LDL fraction (mean +/- S.D.; 1.61 +/- 0.11 vs. 1.52 +/- 0.13, respectively; P = 0.003). Increased cholesterol content in LDL was mainly due to free cholesterol. No differences were detected between the two groups in the frequency of LDL pattern A (major LDL peak > 255 A) and pattern B (major LDL peak < or = 255 A). However, a higher frequency of LDL pattern B was found in NIDDM patients with low plasma total triglyceride concentrations ( < 150 mg/dl) compared to the to the control subjects (45% vs. 7%, P = 0.02). Thus in normolipidemic patients with mild NIDDM, the major lipoprotein abnormalities were a low level of HDL cholesterol and compositional changes in LDL and VLDL + IDL fractions. Compositional abnormalities included enrichment of apo B-containing lipoproteins with cholesterol. These lipoprotein abnormalities could have atherogenic potential in patients with mild NIDDM and normolipidemia.

The effects of lipid lowering drugs on metabolic control and lipoprotein composition in type 2 diabetic patients with mild hyperlipidaemia

Patients with Type 2 diabetes are at increased risk from macrovascular disease whether or not they are hyperlipidaemic. Several factors may contribute to this increased risk including abnormalities of lipoprotein composition. The aim of our study was to determine the effects of lipid lowering drugs on lipoprotein composition (lipoprotein fractions were separated by sequential flotation ultracentrifugation) and insulin sensitivity (measured by a modified Harano technique) in 44 patients with mild hyperlipidaemia. All patients had total cholesterol concentrations between 5.2 and 6.5 mmol l-1 and total triglyceride concentrations < 3.0 mmol l-1, and were randomized by minimization to receive treatment for 12 weeks with bezafibrate, acipimox, simvastatin or placebo. Total cholesterol concentrations were decreased by simvastatin, 5.7 +/- 0.4 to 3.7 +/- 0.6 mmol l-1 (p < 0.05), due mainly to reduced LDL-cholesterol levels (-1.25 mmol l-1; p < 0.05), and bezafibrate 5.7 +/- 0.6 to 4.6 +/- 0.4 mmol l-1 (p < 0.05). The LDL:HDL-cholesterol ratio was reduced in the simvastatin group 2.0 +/- 0.5 to 1.2 +/- 0.3 (p < 0.005). There was no effect of the drugs on glycated haemoglobin or insulin sensitivity. In conclusion bezafibrate and simvastatin improve the lipid profile in Type 2 diabetic patients without adversely affecting diabetic control.

Fasting and postprandial determinants for the occurrence of small dense LDL species in non-insulin-dependent diabetic patients with and without hypertriglyceridaemia: the involvement of insulin, insulin precursor species and insulin resistance

We have studied low density lipoprotein (LDL) subclass distribution in a group of male patients with non-insulin-dependent diabetes mellitus (NIDDM) and investigated its relationships to fasting and postprandial triglyceride (TG)-rich lipoproteins, insulin resistance, lipoprotein lipase (EC 3.1.1.3; LPL), hepatic lipase (EC 3.1.1.34; HL), lecithin:cholesterol acyl transferase (EC 2.3.1.43; LCAT) and cholesteryl ester transfer protein (CETP) activities. LDL was subfractionated by density gradient ultracentrifugation. Postprandial lipoproteins were measured after an oral fat load using retinyl palmitate as a marker for intestinal TG-rich lipoproteins. Hypertriglyceridaemic NIDDMs (HTG) had a preponderance of small dense LDL particles present in the plasma and reduced amounts of large buoyant species when compared to normotriglyceridaemic patients (NTG) and controls. Both groups of diabetics were more insulin resistant than the controls (P < 0.05) and had raised concentrations of proinsulin (P < 0.05), although insulin content did not differ significantly. 32-33 split proinsulin (SPI) was the major insulin-like molecule present in HTG and was present in significantly higher amounts in these patients (P < 0.05) than either NTG or control subjects and correlated significantly with the presence of small dense LDL particles. After a test meal, the postprandial chylomicron response was greater in HTG than either NTG diabetics or controls (P < 0.05). Chylomicron remnants were present to a greater extent in HTG than in NTG and controls (P < 0.05), although in this case NTG also contained more chylomicron remnants than control subjects (P < 0.05). There was no difference in the LPL activity, CETP and LCAT between diabetics and controls, whereas an increase in hepatic lipase activity was seen in the HTG diabetics (P < 0.05). Both CETP and LCAT activities increased postprandially. Multivariate analysis showed that TG, HDL content and HL activity were the most important determinants of small dense LDL concentration in the fasting state (R2 = 67%). Postprandially, chylomicron remnant clearance, HL and insulin resistance were the major determinants (R2 = 61%) of LDL-III.

LDL particle size in mildly hypertriglyceridemic subjects: no relation to insulin resistance or diabetes

We examined 18 Type 2 diabetic and 19 non-diabetic subjects in order to determine the association between insulin resistance and LDL particle size distribution in mildly hypertriglyceridemic and hyperinsulinemic subjects with and without Type 2 diabetes. Insulin sensitivity of the patients was characterized by their insulin-stimulated glucose uptake rate determined by euglycemic clamp technique. LDL particle size distribution was determined by nondenaturing polyacrylamide gradient gel electrophoresis. Type 2 diabetic and non-diabetic subjects had closely similar serum lipid and lipoprotein concentrations as well as the mean particle diameters of the major LDL peak (246 +/- 6 A and 244 +/- 6 A, respectively). To evaluate the effect of insulin resistance on LDL particle size the participants were categorized into two subgroups using the median of their insulin-stimulated glucose uptake rate (14.67 mumol/kg/min) as a cut-off point. Neither lipid and lipoprotein concentrations nor the LDL particle size distributions differed between the more insulin resistant group (nine diabetic and nine non-diabetic subjects) and less insulin resistant group (nine diabetic and ten non-diabetic subjects). LDL particle size was not associated with the insulin-stimulated glucose uptake rate or with the mean 24-h concentration of serum insulin. Mean 24-h concentration of serum triglycerides was the strongest discriminator for LDL particle size (r = -0.44, P < 0.01). In conclusion, neither Type 2 diabetes nor insulin resistance seem to have any direct effect on LDL particle size in mildly hypertriglyceridemic subjects. The fact that LDL particle size was associated with serum triglycerides indicates that the effect of diabetes and insulin resistance on LDL particle size could be explained by the effects of insulin resistance and/or hyperinsulinism on VLDL metabolism.

Factors influencing the low density lipoprotein profile in type 2 diabetic patients

The lipoprotein distribution profile was examined in Type 2 (non-insulin-dependent) diabetic patients (n = 52), with particular emphasis on factors influencing low density lipoproteins (LDL). Triglycerides were negatively correlated with LDL-2 (r = 0.34, p < 0.05) and positively correlated with smaller, denser LDL-3 (r = 0.57, p < 0.001). This yielded a highly significant, negative correlation between triglycerides and the LDL-2/LDL-3 mass ratio (r = -0.59, p < 0.001) which is an indication of the presence of smaller LDL particles. Parameters of glycaemic control, in the form of fasting blood sugar and glycated haemoglobin (HbA1c), were also negatively correlated with the LDL-2/LDL-3 mass ratio in univariate analyses; both remained significantly correlated with the mass ratio when corrected for triglycerides. Stepwise multiple regression analysis identified a three-parameter model comprising triglycerides, HbA1c, and high density lipoprotein cholesterol as best defining the variations in the LDL-2/LDL-3 mass ratio (adjusted r2 = 0.52). These observations are consistent with an independent impact of diabetes on the LDL distribution profile and the possibility that the latter may be subjected to multiple pathological influences in diabetic patients.

Quantification of human serum paraoxonase by enzyme-linked immunoassay: population differences in protein concentrations

Paraoxonase is a serum protein bound to high-density lipoproteins (HDLs). The physiological function of the enzyme is unknown, but a role in lipid metabolism has been postulated. To date, studies of the protein have had to rely on measurements of enzyme activity with various substrates. We have developed a highly specific, competitive e.l.i.s.a. using a previously characterized monoclonal antibody. The assay can detect 20 ng of paraoxonase with a working range of 75-600 ng. Intra- and interassay coefficients of variation were 6.5 and 7.9% respectively. Serum concentrations of paraoxonase in healthy subjects from Geneva and Manchester ranged from 25 to 118 micrograms/ml. There were significant differences in mean concentrations between the two groups (Geneva, 79.3 +/- 18.7 micrograms/ml; Manchester, 59.9 +/- 24.1 micrograms/ml: P < 0.001), differences also apparent when subjects were compared according to paraoxonase phenotype. These appeared to be largely a consequence of differences in apolipoprotein A-I concentrations between the two populations, suggesting that HDL particle number may be important in determining serum levels of paraoxonase. Paraoxonase specific activities were also significantly different between the two groups of subjects (Geneva, 2.08 +/- 0.96 units/mg; Manchester, 3.08 +/- 1.73 units/mg: P < 0.001), which may reflect differences in HDL particle composition. The e.l.i.s.a. should furnish the necessary complement to studies of paraoxonase enzymic activity and has already provided evidence for differences with respect to serum levels of the protein both between populations and between phenotypes within populations.

Cholesterol rich apo B containing lipoproteins and smoking are independently associated with macrovascular disease in normotensive NIDDM patients

A cross-sectional study of macrovascular disease (MVD) and associated metabolic and other risk factors was conducted in 87 normotensive NIDDM patients. MVD was assessed by Rose questionnaire, 12 lead resting ECG, duplex scanning of carotid and peripheral vessels, and ankle:brachial systolic blood pressure ratio. Fasting serum total cholesterol, total triglycerides, LDL cholesterol, HDL cholesterol, apolipoproteins AI and B, lipoprotein (a), HbA1, plasma glucose, insulin, and C-peptide responses to a carbohydrate rich meal, body mass index (BMI), waist-hip ratio, urinary albumin excretion rate, blood pressure, smoking and family history were assessed as possible 'risk factors'. Apolipoprotein:lipid ratios were calculated to estimate lipoprotein composition. Thirty-six patients had demonstrable MVD. The presence of MVD was associated with higher total triglycerides (p < 0.05), BMI (p < 0.05), systolic blood pressure (p < 0.01), a lower apo B:non HDL cholesterol ratio (p < 0.001), and smoking (p < 0.005) but no other measures. Multiple regression analysis revealed smoking and a low apo B:non HDL cholesterol to be independently associated with MVD. The low apo B:non HDL cholesterol suggests a high cholesterol content of apo B containing lipoproteins. This lipoprotein abnormality is not a feature of NIDDM, but when present in these patients may be particularly atherogenic.

Diabetic dyslipidemia

Diabetes is associated with increased morbidity and mortality from cardiovascular disease in the absence of the major risk factors: cigarette smoking, hypertension, and serum cholesterol concentration. When these risk factors are present, the attributable risk to each factor alone and to the combination of risk factors is higher in diabetics than in nondiabetics. Thus, stringent measures to correct risk factors for cardiovascular disease have been advocated in diabetic patients. In addition to hypercholesterolemia, other lipid and lipoprotein abnormalities collectively referred to as diabetic dyslipidemia are likely to contribute to vascular risk. Hypertriglyceridemia often associated with low high-density lipoprotein cholesterol is common in non-insulin-dependent diabetes mellitus patients and is associated with insulin resistance. Recent information in diabetic patients pointing to the association of hypertriglyceridemia with accumulation of remnant particles and alterations in low-density lipoprotein subfractions helps to explain the strong relationship between hypertriglyceridemia and vascular risk in these individuals. Although there are as yet no intervention trials with lipid-lowering diets or drugs in diabetic patients to judge the impact on vascular disease, national and international bodies have furnished guidelines for the identification and treatment of lipid disorders in diabetes in the hope of reducing the huge toll of vascular disease in these patients.

Low-density lipoprotein particle size in type 2 diabetic patients and age matched controls

Non-enzymatic glycation of low-density lipoprotein (LDL), and the predominance of small dense LDL particles may together contribute to the increased risk of atherosclerosis in diabetes. We aimed to establish whether the size of LDL particles is related to plasma triglyceride concentration, and to the extent of LDL glycation in type 2 diabetic patients. Sixteen men with type 2 diabetes and 16 age matched non-diabetic controls were studied. LDL size was measured by rapid density gradient ultracentrifugation, and LDL glycation by affinity chromatography. Modal LDL density correlated with plasma triglyceride concentrations in both diabetic and control groups (r = 0.86, P < 0.0001, and r = 0.76, P < 0.0008, respectively). There was no significant difference in these variables between the groups. LDL modal density showed no correlation with HbA1, serum fructosamine or plasma glucose in either group. In the diabetic group the degree of LDL glycation correlated with serum fructosamine (r = 0.74, P < 0.001), HbA1 (r = 0.65, P < 0.008), and with plasma glucose (r = 0.64, P < 0.008). Our results suggest that, in well controlled type 2 diabetic patients LDL size is independent of short-term glycaemic control but can be predicted by plasma triglyceride concentrations.

Lipoprotein disorders in diabetes mellitus

In IDDM or NIDDM, the total plasma cholesterol and triglycerides are usually within normal limits when the blood glucose is controlled. Marked hypertriglyceridemia can develop with loss of glycemic control and is often due to superimposed genetic abnormalities in lipoprotein metabolism. Tight control in IDDM usually reduces LDL and VLDL to normal levels and may raise HDL above the normal range. Low HDL cholesterol and mild to moderate elevations of VLDL triglyceride are common in NIDDM if obesity or proteinuria is also present. Both HDL and LDL may be smaller and more dense and may be enriched with triglyceride as compared with cholesterol. These abnormalities may require weight loss for control. The increased incidence of cardiovascular disease in diabetes is unexplained but is amplified by the well-defined cardiovascular risk factors. The new American Diabetes Association guidelines call for treatment of high triglycerides and LDL cholesterol to be aggressively reduced. Triglycerides should be under 200 mg/dL, are considered borderline high between 200 and 400 mg/dL, and high when above 400 mg/dL. Low HDL is defined as less than 35 mg/dL. Control of obesity with diet and exercise and reduced intake of saturated fat and cholesterol are important first steps. If needed, drug therapy is appropriate to reduce LDL to levels below 130 mg/dL in all adult diabetics and below 100 mg/dL in those with cardiovascular disease.

Underexpression of the apolipoprotein E4 isoform in an Italian population

Apolipoprotein (apo) E polymorphism was examined in a population of Italian blood donors. A significantly reduced frequency of the epsilon 4 allele was observed in comparison to a combined Caucasian population. Apo E polymorphism was also associated with significant differences in plasma lipid and lipoprotein levels. Notably, total and low-density lipoprotein cholesterol as well as triglycerides were increased, whereas high-density lipoprotein cholesterol was decreased in carriers of the E4 isoform. This is the first report of a significantly lower frequency of the apo E4 isoform in a European population. The reduced occurrence of an apo E isoform, which is associated with a more atherogenic lipid/lipoprotein profile, may be a contributory factor to the relatively lower incidence of cardiovascular disease in the Italian population.

Lipids and lipoproteins predicting coronary heart disease mortality and morbidity in patients with non-insulin-dependent diabetes

BACKGROUND

The aim of this study was to investigate the association of lipoprotein fractions with the future risk of coronary heart disease (CHD) in patients with non-insulin-dependent diabetes (NIDDM).

METHODS AND RESULTS

At baseline, lipoprotein fractions were determined in 313 diabetic patients with NIDDM (153 men and 160 women), and these patients were followed up for 7 years with respect to CHD events (CHD death or all CHD events including CHD death or nonfatal myocardial infarction). Altogether, 56 NIDDM patients (28 men and 28 women) died from CHD and 25 had a nonfatal myocardial infarction (17 men and 8 women) during the follow-up. NIDDM patients having these CHD events during the follow-up had higher levels of total and very-low-density lipoprotein (VLDL) triglycerides and VLDL cholesterol and lower levels of high-density lipoprotein (HDL) and HDL2 cholesterol than those without CHD events. The risk for CHD death was fourfold and for all CHD events, twofold higher among diabetics with low HDL cholesterol (< 0.9 mmol/L) than among diabetics with HDL cholesterol > or = 0.9 mmol/L. High triglyceride level (> 2.3 mmol/L) was associated with a twofold increase in the risk of CHD events. In multiple logistic regression analyses, HDL was inversely associated with CHD events and VLDL triglycerides with CHD events in NIDDM patients with low HDL cholesterol level (< or = 1.12 mmol/L).

CONCLUSIONS

Our 7-year follow-up study gives evidence that low HDL and HDL2 cholesterol, high VLDL cholesterol, and high total and VLDL triglycerides are powerful risk indicators for CHD events in patients with NIDDM:

Lipoprotein compositional abnormalities and insulin resistance in type II diabetic patients with mild hyperlipidemia

Lipoprotein composition was determined using ultracentrifugation in 20 non-insulin-dependent (NIDDM) diabetic patients on diet only (D), 20 NIDDM patients on diet and sulfonylurea therapy (T), and 20 nondiabetic control subjects (C), all of whom had total plasma cholesterol concentrations < 6.5 mmol/L and total plasma triglyceride concentrations < 3.0 mmol/L. Although the groups were well matched for age, body mass index, total triglyceride levels, and total cholesterol concentrations, there were significant compositional abnormalities in the low-density lipoprotein (LDL) fractions of diabetic subjects. The LDL total lipid to apolipoprotein B weight ratio (representing the density distributions of LDL particles) was reduced in both diabetic groups: 3.75 +/- 0.3, 3.50 +/- 0.28, and 3.54 +/- 0.22 in C, D, and T groups, respectively (mean +/- SD; P < .05). This was associated with a significant shift in the hydrated density distributions of LDL in the diabetic groups, with the average peak densities being 1.0320 g/mL (in C), 1.0365 g/mL (in D), and 1.0380 g/mL (in T) (P < .05). The LDL particles were also smaller in the NIDDM patients: 21.1 +/- 0.7, 20.4 +/- 0.5, and 20.6 +/- 0.5 nm in C, D, and T groups, respectively (P < .05). When the NIDDM groups were analyzed together, the LDL peak density was found to correlate with both insulin resistance (measured by a modified Harano technique; r = 0.37, P < .015) and total triglyceride concentrations (r = 0.40, P < .01). The results show that diabetic patients have small, dense LDL particles, which may be related to insulin resistance, and that these occur with minimal elevations of total triglyceride concentrations. These potentially atherogenic changes may contribute to the increased coronary heart disease in diabetic patients with mild hyperlipidemia.

The regulation of post-prandial cellular cholesterol metabolism in type 2 diabetic and non-diabetic subjects

The purpose of the study was to determine the effect of diabetes on the regulation of postprandial cholesterol metabolism. Four groups of patients (n = 8 for each group) were examined: Type 2 diabetic patients with and without hypercholesterolaemia and non-diabetic subjects with and without hypercholesterolaemia. Serum lipoproteins, lipoprotein composition, cellular cholesterol, and cellular cholesterol synthesis were measured before and 4 h after a high calorie meal. The BMI for the hypercholesterolaemic diabetic patients of 31.5 +/- 0.95 (SEM) was significantly higher than that for the control group of 26.2 +/- 1.0 (p < 0.01). Fasting triglyceride levels were significantly higher in the normocholesterolaemic and hypercholesterolaemic diabetic patients and in the hypercholesterolaemic non-diabetic subjects (1.45 +/- 0.22, 2.27 +/- 0.34, and 1.58 +/- 0.18 mmol l-1, respectively) compared with normocholesterolaemic non-diabetic subjects (0.75 +/- 0.12 mmol l-1: p < 0.01). The normocholesterolaemic and hypercholesterolaemic diabetic subjects had significantly lower fasting serum high density lipoprotein (HDL) (1.06 +/- 0.08 and 1.04 +/- 0.06 mmol l-1) compared to the corresponding non-diabetic groups (1.29 +/- 0.11 and 1.45 +/- 0.17 mmol l-1, p < 0.05). The esterified/free cholesterol ratio of very low density lipoprotein (including chylomicrons VLDL-C) decreased postprandially in all groups with an overall decrease of 1.33 to 0.83 (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a distinct human high-density lipoprotein subspecies defined by a lipoprotein-associated protein, K-45. Identity of K-45 with paraoxonase

In an attempt to provide immunological tools for subfractionation of high-density lipoproteins (HDL), monoclonal antibodies were raised against HDL complexes. Two clones identified a peptide, provisionally named K-45 (pI 4.5-4.9; molecular mass 45 kDa, range 42-48 kDa), whose plasma distribution and lipoprotein association were fully characterised. Gel filtration localised the peptide to the HDL region of human plasma where it co-eluted with apolipoprotein (apo) A-I, the structural protein of HDL. Complementary studies employing immunoabsorption with anti-(apo A-I) antibodies removed 90% of K-45 from plasma: conversely, anti-(apo A-II) antibodies eliminated only 10% of K-45. Immunoaffinity chromatography on an anti-(K-45) column revealed that the peptide was present in a distinct HDL subsepecies containing three major proteins: K-45, apo A-I and clusterin or apo J. The lipoprotein nature of the bound fraction was indicated by electron microscopy (diameter 9.6 +/- 3.3 nm) and quantification of lipids, the latter showing an unusually high triacyglycerol concentration. Plasma concentrations of K-45 were positively correlated with apo A-I and HDL-cholesterol and negatively correlated with apo B and total cholesterol. Thus, the peptide appears to be linked, directly or indirectly, to processes which give rise to an anti-atherogenic lipid profile. After completion of the present studies, an N-terminal sequence identical to that of K-45 was reported in recently isolated cDNA clones. These clones encode paraoxonase.

The effect of low density lipoprotein composition on the regulation of cellular cholesterol synthesis: a comparison in diabetic and non-diabetic subjects

This study investigates compositional differences in low density lipoprotein (LDL) subfractions and their relationship to cellular cholesterol synthesis. We examined ten normocholesterolaemic (serum cholesterol < 6.5 mM) non-diabetic subjects (group 1) and compared them with ten normocholesterolaemic (group 2) and ten hypercholesterolaemic (group 3) (serum cholesterol > 6.5 mM) type 2 (non-insulin-dependent) diabetic patients. Serum cholesterol levels for groups 1, 2 and 3 were 5.19 +/- 0.27, 5.20 +/- 0.27 and 7.51 +/- 0.31 mM. LDL (density 1.006-1.028 g/l) and LDL2 (1.028-1.063 g/l) were isolated by density gradient ultracentrifugation. A significantly greater proportion of cholesterol was carried in LDL2 than LDL1 in all groups. There was a significantly lower cholesterol/protein ratio in LDL1 from the hypercholesterolaemic diabetic patients compared with controls. The LDL esterified/free cholesterol ratio was significantly greater in both LDL1 and LDL2 in the hypercholesterolaemic diabetic patients compared with the other two groups. There was a negative correlation between inhibition of cholesterol synthesis and the esterified/free cholesterol ratio of both LDL1 (r = 0.56, P < 0.002) and LDL2 (r = 0.63, P < 0.001). Cellular cholesterol of 41.0 +/- 0.3 microgram/mg cell protein in the hypercholesterolaemic diabetic patients was also significantly higher compared with values of 30.32 +/- 2.0 and 34.1 +/- 4.2 micrograms/mg cell protein for the normocholesterolaemic non-diabetic and diabetic groups. In vitro LDL esterification led to a decrease in LDL receptor-mediated binding and resulted in a 40% reduction in the ability of the LDL to suppress cholesterol synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

LDL subclass phenotypes and triglyceride metabolism in non-insulin-dependent diabetes

Plasma low density lipoprotein (LDL) comprises multiple discrete subclasses differing in size, density, and chemical composition. A common, heritable phenotype characterized by the predominance of small, dense LDL particles (LDL subclass phenotype B) is associated with relatively increased concentrations of plasma triglycerides, reduced levels of high density lipoprotein, and increased risk of coronary artery disease in comparison with subjects with larger LDL (LDL subclass phenotype A). Population studies have indicated that approximately 20-30% of adult men have phenotype B, and another 15-20% have LDL of intermediate size. The lipid changes in phenotype B are similar to those that have been observed in patients with non-insulin-dependent diabetes mellitus (NIDDM). In the present study, we have assessed LDL subclass phenotypes in normolipidemic men with NIDDM and in age-matched control subjects who had similar lipid levels. There was a greater than twofold increase in the percentage of individuals with the LDL B phenotype in the NIDDM subjects. The LDL B phenotype was associated with higher plasma triglyceride levels and a trend toward lower high density lipoprotein cholesterol levels compared with the LDL A phenotype in the NIDDM subjects, as has been previously observed in control groups. Indices of diabetic control, such as fasting and hemoglobin A1 levels, were similar regardless of LDL phenotype pattern, suggesting that glycemic control was not likely to account for the increase in the LDL B phenotype. In both control and NIDDM subjects, the clearance of triglyceride-rich lipoproteins was slowed in the subjects with the LDL phenotype B compared with those with the A phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)