Marked changes of lipid levels during puberty in a patient with lipoprotein lipase deficiency.

UNLABELLED: Clinical and biochemical characteristics of a female patient with familial lipoprotein lipase deficiency have been followed in short intervals before and during puberty. The proband is compound heterozygote for two missense mutations in the lipoprotein lipase gene. One mutation occurs in codon 250 (Asp250-->Asn), the other is in codon 410 (Glu410-->Lys). The residual lipoprotein lipase activity in the proband is less than 10% of controls. Before puberty the proband usually presented with moderate isolated hypertriglyceridaemia. During the initial phase of puberty a dramatic increase in the plasma concentration of both cholesterol and triglycerides was observed. During the second half of puberty a reduction of cholesterol but not of triglycerides was noticed. CONCLUSION: These findings show that the phenotypic expression of familial chylomicronaemia can be modified to a large extent by hormones. Furthermore they demonstrate the need for a closer clinical observation of type I patients during puberty.

Lipoprotein (a) and vascular disease in diabetic patients.

In order to assess the potential role of lipoprotein (a) as a risk factor for cardiovascular disease in diabetes mellitus, plasma concentrations were measured in a large group (n = 500) of non-insulin-dependent (NIDDM, n = 355) and insulin-dependent (IDDM, n = 145) patients. Concentrations of lipoprotein (a) were compared in diabetic patients with (n = 153) or without (347) documented vascular disease (ischaemic heart disease, peripheral vascular disease or macroangiopathy). They were significantly higher (p < 0.05) in patients with ischaemic heart disease (mean [interquartile range] 15.5 (5.0-38.0) vs 9.0 (4.5-26.0) mg/dl) or macroangiopathy (13.0 (5.0-38.0) vs 9.0 (4.0-25.0) mg/dl) compared to patients without manifestations of vascular disease. In addition, stepwise logistic regression analysis identified lipoprotein (a) levels > or = 30 mg/dl as being independently associated with the presence of cardiovascular disease. Lipoprotein (a) was an independent risk factor for ischaemic heart disease and macroangiopathy in this group of IDDM and NIDDM patients.

Apolipoprotein E polymorphism as a risk factor for vascular disease in diabetic patients.

OBJECTIVE: To examine the prevalence of cardiovascular disease in diabetic patients as a function of apolipoprotein (apo) E polymorphism. RESEARCH DESIGN AND METHODS: The apo E phenotypes and plasma lipid, lipoprotein, and apo levels were determined for 517 Italian diabetic patients. The prevalence of cardiovascular disease (defined as ischemic heart disease [HD] and/or peripheral vascular disease and/or cerebrovascular disease) was assessed as a function of apo E polymorphism at entry and after 4 years. RESULTS: The occurrence of vascular disease did not differ significantly between diabetic patients in the various categories of apo E phenotype either at entry into the study or after 4 years. When expressed as a percentage of patients with disease, we observed--for E2, E3, and E4 carriers, respectively--at entry: IHD, 20.0% (n = 14), 21.0% (n = 79), and 21.5% (n = 14); and macroangiopathy, 24.3% (n = 17), 29.3% (n = 110), and 24.6% (n = 16). Apo E polymorphism did not make a significant contribution to multiple logistic regression models designed to identify the factors associated with the occurrence of vascular disease in diabetic patients. CONCLUSION: Apo E polymorphism and, notably, the apo E4 allele cannot be universally considered as a particular risk factor for cardiovascular disease in diabetic patients.

Characterization of subpopulations of lipoprotein particles isolated from human cerebrospinal fluid.

The aim of the present study was to define lipoprotein complexes within cerebrospinal fluid (CSF) in terms of their apolipoprotein composition, using fractionation procedures considered optimal for maintaining lipoprotein structural integrity. Five apolipoproteins were identified, namely apolipoproteins A-I, A-IV, D, E and J. These were differentially distributed amongst lipoprotein particles of which three major subpopulations were identified. CSF-LpAI (20.1 +/- 3.8 nm) was enriched in apolipoprotein A-I and contained the major proportion (> 50%) of apolipoproteins D, E and J. CSF-LpE, of similar size to CSF-LpAI (20.2 +/- 3.1 nm), was composed principally of apolipoprotein E, with minor quantities of apolipoproteins A-I, A-IV, D and J. Elimination of these particles from cerebrospinal fluid by immunoabsorption revealed a third subpopulation of significantly greater diameter (32.0 +/- 6.8 nm). The majority (62%) of apolipoprotein A-IV was also present in this fraction. The study demonstrates the structural and size heterogeneity of lipoproteins in cerebrospinal fluid. This may reflect the lipid transport processes within the central nervous system.

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.

Postprandial lipemia differentially influences high density lipoprotein subpopulations LpAI and LpAI,AII.

The behavior of apolipoprotein-defined subpopulations LpAI and LpAI,AII within high density lipoprotein (HDL) subclasses 2 and 3 was analyzed in the postprandial phase after a fat load. For the whole group of subjects, increases in plasma concentrations of HDL, principally due to the influx of lipoprotein surface components, were largely confined to the HDL3 density range and involved LpAI,AII and LpAI. However, the degree of postprandial lipemia influenced the distribution of surface remnants between the subfractions. In subjects with a limited postprandial rise in triglycerides, increased HDL mass was predominantly associated with LpAI,AII, and equally distributed between HDL2 and HDL3. Conversely, subjects with exaggerated postprandial lipemia manifested increased mass primarily within the HDL3 density range, implicating both LpAI,AII and LpAI. Stepwise regression analysis identified a two-variable model, involving LpAI,AII within HDL2 and LpAI within HDL3, as best defining the relationship between postprandial lipemia and the increase in HDL mass. Postprandial increases in triglyceride content were observed for all HDL subfractions, whilst modifications to the core lipid mass ratios were significant only for LpAI,AII. Stepwise regression analysis revealed a significant correlation between postprandial lipemia and the increase in triglyceride concentration only of LpAI,AII within HDL3. The results suggest that postprandial lipemia differentially influences apolipoprotein-defined HDL subfractions. The extent of postprandial lipemia may determine the involvement of different HDL subfractions in postprandial lipoprotein metabolism.

The effect of the gastrointestinal lipase inhibitor, orlistat, on serum lipids and lipoproteins in patients with primary hyperlipidaemia.

The effect of orlistat, a nonabsorbed inhibitor of gastric and pancreatic lipases, was examined in patients with primary hyperlipidaemia (serum cholesterol > or = 6.2 mmol.l-1 and triglycerides < or = 5.0 mmol.l-1) not responsive to dietary change alone. In a multicentre, randomised, double-blind study, 103 men and 70 women received 30, 90, 180, or 360 mg or orlistat or placebo for 8 weeks. Total and low-density lipoprotein cholesterol levels were reduced by 4% and 5% with 30 mg orlistat, by 7% and 8% with 90 mg orlistat, by 7% and 7% with 180 mg orlistat and by 11% and 10% with 360 mg orlistat compared to placebo. High density lipoprotein cholesterol levels significantly decreased in the 360 mg orlistat group. Triglyceride levels significantly increased in the placebo group but not in the drug groups. Body weight decreased by 1.2 kg with 360 mg orlistat, despite a weight maintenance diet. Decreases in vitamin E and D levels occurred, although both vitamins remained within the normal range. Adverse effects from the gastrointestinal tract were frequent, but led to discontinuation of therapy in only seven patients. Orlistat is a new therapeutic drug for the treatment of hyperlipidaemia that may be particularly useful among overweight patients. Its potential place in therapy will await long-term studies. Vitamin supplementation should be considered during treatment.

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.

[Comparison of 2 cholesterol synthesis inhibitors (simvastatin and pravastatin)]. / Comparaison de deux inhibiteurs de la synthèse du cholestérol (simvastatine et pravastatine).

Inhibitors of cholesterol synthesis (HMG-CoA reductase) are the most effective cholesterol-lowering drugs. Comparison of several studies in the literature suggests that simvastatin is approximately twice as effective as pravastatin on a milligram basis. These results are confirmed by the present study, which compares treatment with simvastatin (10 mg/d) with pravastatin (20 mg/d) in the same hypercholesterolemic patients (n = 17). The reduction in LDL cholesterol is the same with twice the dose of pravastatin as with simvastatin (26 +/- 3% vs 27 +/- 2% respectively). The reductions in atherogenic ratios, total cholesterol, HDL cholesterol and ApoB/ApoA1 are similar. Undesirable effects are rare and comparable. The differences between the two inhibitors appear to be on the molecular level, in tissue selectively and regarding in vivo efficacy.

Topical timolol maleate might adversely affect serum lipoproteins.

Conflicting observations have been reported about the effects of topically administered timolol maleate on serum lipoproteins. We therefore considered this issue in a series of eight glaucoma patients receiving timolol maleate. Cholesterol and triglycerides were measured in plasma and in low-density lipoproteins (LDL), and high-density lipoproteins (HDL), both before and following three months of treatment. Following the treatment, the mean atherogenic index was increased from 2.72 to 3.38 (p = 0.012). This suggests that the atherogenic index should be determined before and during timolol maleate treatment in high-risk cardiovascular patients.

Gender differences in a type 2 (non-insulin-dependent) diabetic population with respect to apolipoprotein E phenotype frequencies.

Apolipoprotein E polymorphism was examined in an Italian population of Type 2 (non-insulin-dependent) diabetic patients. There were significant differences (p < 0.05) in allele frequencies between male and female patients due to an under-representation of the E4 allele in the female group. No differences in allele frequencies were noted when non-diabetic male and female control subjects were compared. Both control groups exhibited similar allele distributions to that of male diabetic patients, but were significantly different (p < 0.05) from female diabetic patients. A closer examination of the female diabetic population revealed that under-representation of the E4 allele was principally confined to patients aged 60 years or older. This subgroup showed a significantly different (p < 0.05) allele frequency profile from control subjects (both men and women) and diabetic men, whereas this was not observed in the younger diabetic women (< or = 59 years). The results are consistent with the suggestion that the E4 allele may be a particular risk factor for female diabetic patients.

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.

Characterization of a human high density lipoprotein-associated protein, NA1/NA2. Identity with SP-40,40, an inhibitor of complement-mediated cytolysis.

Two peptides, NA1 and NA2, which we previously suggested to be associated with high density lipoproteins (HDLs), have been purified. Polyclonal antibodies against each peptide and a monoclonal antibody against NA2 have been used to further characterize them and their association with HDL. Immunoblotting studies revealed that the peptides form a complex of molecular mass of approximately 80 kd. Agarose gel filtration showed coelution of NA1/NA2 and apolipoprotein (apo) A-I, the structural protein of HDL. This was confirmed by fast protein liquid chromatography, which further indicated that up to 60% of NA1/NA2 was located within the lower density range of the HDL spectrum. Complementary studies with anti-apo A-I immunoaffinity columns provided evidence that at least 40% of NA1/NA2 was associated with HDL, an association easily disrupted by ultracentrifugal manipulation. Finally, partial amino acid sequences showed virtually complete homology with a recently identified protein, SP-40,40, or cytolysis inhibitor. The protein is suggested to have a powerful inhibitory effect on complement-mediated cell lysis. Our results could thus furnish an explanation for the previously observed modulating influence of HDL on complement activity.