Differential effect of hormone therapy and tibolone on lipids, lipoproteins, and the atherogenic index of plasma

The aim of our study was to assess the effect of various regimens and doses of hormone therapy and tibolone on the Atherogenic Index of Plasma (AIP). A total of 519 postmenopausal women attending our menopause clinic were studied in a prospective design. Women with climacteric symptoms were randomly assigned to receive 1 of the following regimens: tibolone 2.5 mg, conjugated equine estrogens 0.625 mg plus medroxyprogesterone acetate 5 mg (CEE/MPA), 17beta-estradiol 2 mg plus norethisterone acetate 1 mg (E2/NETA), or 17beta-estradiol 1 mg plus norethisterone acetate 0.5 mg (low E2/NETA). Serum parameters were assessed at baseline and after 6 months and included total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, apolipoprotein A1 and apolipoprotein B. The AIP was assessed as the log (triglycerides [mmol/L]/HDL-C [mmol/L]). CEE/MPA treatment associated with lower mean LDL-C but higher mean triglyceride levels (-15.5 mg/dL +/- 3.6, P = 0.0001; 12.6 mg/dL +/- 4.8, P = 0.01). Furthermore, CEE/MPA treatment resulted in higher AIP levels (0.073 +/- 0.021, P = 0.001). On the contrary, both E2/NETA regimens and tibolone associated with lower mean triglyceride and HDL-C levels (E2/NETA, triglycerides: -9.8 mg/dL +/- 5.0, P = 0.049; HDL-C: -4.9 mg/dL +/- 1.8, P = 0.01, low E2/NETA triglycerides: -12.5 mg/dL +/- 4.1, P = 0.003; HDL-C: -4.7 mg/dL +/- 1.3, P = 0.001; tibolone, triglycerides: -21.9 mg/dL +/- 2.7, P = 0.0001; HDL-C: -12.7 mg/dL +/- 1.1, P = 0.0001). None of the 3 regimens had any effect on AIP. The effect of a particular regimen of hormone therapy on the lipid-lipoprotein profile differs depending on the parameter assessed. The use of unified markers such as AIP will be helpful in evaluating the overall effect of lipid-lipoprotein modulation on the cardiovascular system. In fact, the concurrent assessment of the therapy effect on both LDL-C and AIP may be more dependable in evaluating the cardiovascular impact of a given regimen.

Long-term efficacy and safety of a new olive oil-based intravenous fat emulsion in pediatric patients: a double-blind randomized study

BACKGROUND

A new intravenous lipid emulsion (ILE) prepared from a mixture of soybean and olive oils contains only long-chain triacylglycerols, with a low proportion (20%) of polyunsaturated fatty acids and 60% monounsaturated fatty acids.

OBJECTIVE

The goal of this randomized, double-blind clinical trial was to assess in children the efficacy and safety of this new ILE compared with a control group receiving a soybean-oil emulsion.

DESIGN

Eighteen children received for 2 mo 24% of nonprotein energy (1.80 g kg (-)(1) d(-)(1)) either as the new ILE or a soybean oil-based emulsion. Assessments were performed on days -30, 0, 30, and 60 and the changes (day 60 - day 0) assessed by analysis of variance.

RESULTS

There were no significant differences in triacylglycerol, apolipoproteins A-I and B, or HDL cholesterol between the 2 groups, whereas total and LDL cholesterol were higher in the soybean oil group on day 60. The pattern of 20:4n-6 in erythrocyte membranes did not change significantly, nor did the ratio of 20:3n-9 to 20:4n-6. On day 60, 18:1n-9 was significantly higher in the olive oil group, the ratio of Sigma(n)-6 > C(18) + 18:3n-6 to 18:2n-6 was 2.20 +/- 0.09 in the olive oil group and 1.33 +/- 0.16 in the soybean-oil group, and Sigma(n)-3 > C(18) was 3.83 +/- 0.30 in the olive oil group and 4. 03 +/- 0.33 in the soybean-oil group. The peroxidation index was lower after the olive oil treatment.

CONCLUSIONS

The olive oil-based emulsion was well tolerated, maintained a normal EFA status, and may be more suitable for prevention of lipid peroxidation than the soybean-oil-based emulsion.

Increased Ability of LDL from Normolipidemic Type 2 Diabetic Women to Generate Peroxides

Background: We assessed the ability of LDL from 30 type 1 diabetic patients (18 men, 12 women), 65 type 2 diabetic patients (35 men, 30 women), and 35 controls (19 men, 16 women) to generate peroxides. The men and women in the diabetic groups were studied separately and matched for age, body mass index, duration of diabetes, glycohemoglobin, and conventional lipid characteristics according to the presence or absence of hyperlipidemia.

Methods: The ability of LDL to form peroxides was assessed by measuring the thiobarbituric acid-reactive substances corrected for LDL-cholesterol [ratio of malondialdehyde (MDA) to LDL-cholesterol]. LDL particle size was expressed as the ratio of LDL-cholesterol to apolipoprotein B (LDL-cholesterol/apoB).

Results: The MDA/LDL-cholesterol ratio was higher in type 1 and type 2 diabetic patients with hyperlipidemia than in controls. The MDA/LDL-cholesterol ratio was also higher in type 2 normolipidemic women than in controls (P <0.01). The LDL-cholesterol/apoB ratio was lower in type 2 diabetic women than in type 2 diabetic men (P <0.05). The MDA/LDL-cholesterol ratio was negatively correlated with the LDL-cholesterol/apoB ratio (r = −0.78, P <0.001) in hyperlipidemic type 1 (not type 2) diabetic patients. In normolipidemic type 2 diabetic patients, the MDA/LDL-cholesterol ratio was also negatively correlated with the LDL-cholesterol/apoB ratio (r = −0.75, P <0.001) because of the highly significant negative correlation in type 2 diabetic women (r = −0.89, P <0.01).

Conclusions: LDL from well-controlled type 2 diabetic women is smaller and more prone to form peroxides. This could explain why diabetic women are at greater risk of cardiovascular disease.

Performance of a direct, immunoseparation based LDL-cholesterol method compared to Friedewald calculation and a polyvinyl sulphate precipitation method

The analytical performance of a direct, immunoseparation based LDL-cholesterol method (Genzyme Corporation) was evaluated on an ELAN analyser (Merck), and compared with the performance of routinely used methods (LDL-cholesterol estimated by the Friedewald equation, and LDL-cholesterol obtained after polyvinyl sulphate precipitation). Within-day coefficients of variation (CVs) were 0.79 to 2.51% for immunoseparation based LDL-cholesterol; the between-day CVs varied between 2.62 and 3.89%, i.e. within the recommended National Cholesterol Education Program (NCEP) goal of < 4%. A method comparison study, according to the National Committee for Clinical Laboratory Standards (NCCLS) EP9-P guidelines, was performed using fasting normo- and hypertriacylglycerolaemic as well as cholestatic sera. In fresh normotriacylglycerolaemic sera immunoseparation based LDL-cholesterol (y) and Friedewald LDL-cholesterol (x) values were identical as slope and intercept of the Passing & Bablok regression equation were not significantly different from one and zero, respectively (y = 1.006 x -0.107; N = 45). In contrast, immunoseparation based LDL-cholesterol (y) differed significantly from polyvinyl sulphate LDL-cholesterol (x) results (y = 0.922 x + 0.234; N = 103). Freezing normotriacylglycerolaemic sera (three weeks, -20 degrees C) resulted in a negative bias of -5.8% for the immunoseparation based LDL-cholesterol method, and in a positive bias of +5.3% for the polyvinyl sulphate method, compared to fresh specimens. Immunoseparated LDL-cholesterol was completely recovered up to at least 37.84 mmol/l serum triacylglycerols. We conclude that the immunoseparation based LDL-cholesterol method is a practical, not technically demanding technique well applicable within routine clinical laboratories.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between the ratio of serum low-density lipoprotein cholesterol and high-density lipoprotein cholesterol with that of serum apolipoproteins B and A-I

Phosphowolframate/magnesium chloride, a commonly used precipitation method for the determination of high-density lipoprotein cholesterol in human serum, yields a supernatant containing almost all of the lipoproteins apo A-I and apo A-II but no lipoprotein apo B. The correlation between high-density lipoprotein cholesterol and apo A-I was very high (r = 0.94), as well as that between the precipitation method and ultracentrifugal analysis (r > 0.95, P < 0.001). In contrast, detergent precipitation (for the determination of low-density lipoprotein cholesterol in human serum) produced sediments which contained the major proportion of apo B and only minor amounts of apo A-I and apo A-II. The precipitation method for low-density lipoprotein cholesterol showed very good agreement with ultracentrifugal analysis (r = 0.99). Yields of 80.2% were obtained for apo B with both methods. Results obtained using the precipitation methods showed excellent agreement with those obtained using the Friedewald formula (r > 0.99). Results were also very similar when hypertriglyceridemic serum samples were briefly centrifuged before analysis of cholesterol, high-density lipoprotein cholesterol and triglyceride values. The present study shows highly significant correlations between cholesterol/high-density lipoprotein cholesterol or low-density lipoprotein cholesterol/high-density lipoprotein cholesterol and apo B/apo A-I ratios (P < 0.001). Apo B and apo A-I levels could be used in addition to low- and high-density lipoprotein cholesterol values when assessing the risk of cardiovascular disease, if the methods for determining serum apolipoproteins have been properly standardized.

Contents of apolipoprotein A-I, A-II and B of the human serum fractions for high-density and low-density lipoproteins prepared by common precipitation methods

Two common precipitation methods for the determination of HDL-cholesterol in human serum were used, dextran sulphate/MgCl2 and phosphowolframate/MgCl2. They yield supernatants which contained almost all of the apoA-I and apoA-II lipoproteins but no lipoprotein apoB. The correlations between chol-HDL and apoA-I were about the same with these methods (r = 0.79 and 0.80). The correlation between the precipitation methods and ultracentrifugal analysis for chol-HDL was highly significant (r = > 0.95). Correspondingly, two common precipitation methods for the determination of LDL-cholesterol in human serum, buffered heparin, and polyvinyl sulphate procedures, produced sediments, which contained the major proportion of the apoB and only small amounts of apoA-I and apoA-II. However, yields of only 69.0-80.2% were obtained for apoB from the sediments and of 85.8-89.4% from supernatants calculated as the difference from chylomicron free serum. This difference might be due to alterations of the molecular structure of apoB by the precipitation reagents. Comparison of the results with the precipitation methods to those using the Friedewald formula showed excellent agreements (r = > 0.91). Very comparable results were also obtained in the case of marked hypertriglyceridaemia provided that the serum samples were briefly centrifuged before analysis of chol, chol-HDL, and triglyceride values for the formula of chol-LDL. The precipitation methods for chol-LDL showed very good agreement with the values obtained by ultracentrifugal analysis (r = > 0.93). There were no remarkable differences in the correlation of apoB and chol-LDL values measured by different methods (r = 0.85). According to the present results it was found that highly significant correlations existed between chol/chol-HDL or chol-LDL/chol-HDL and apoB/apoA-I ratios (p < 0.001). It is quite evident that apoB and apoA-I values could be used to replace chol-LDL and chol-HDL values when the risk for the cardiovascular diseases is to be assessed.

The measurement of lipoprotein subfractions in plasma using a tabletop ultracentrifuge

We adapted the ultracentrifugation method of the Lipid Research Clinics Program for the separation of lipid subfractions (LDL, VLDL and HDL cholesterol) to a tabletop ultracentrifuge (Beckman TL-100). Centrifugation time was reduced from 18 h to 2.5 h and the sample volume from 5 mL to 2 mL plasma. The imprecision of the LDL-cholesterol estimation (coefficient of variation = CV) was 2.9-7.4% and that of HDL-cholesterol measurement was 1.4-3.9%. Imprecision of the VLDL-C measurement was high (CV = 15.6-29.8%). The results correlated with those obtained by the Lipid Research Clinics method (P less than 0.001). Our method could be conveniently adapted by clinical laboratories serving specialist lipid clinics.

Precipitation of LDL with sulfated polyanions: three methods compared

Three precipitation methods for the determination of low density lipoproteins have been evaluated. In n = 113 normolipidemic samples mean LDL-cholesterol levels have been 2.90 mmol/l, 2.77 mmol/l, 3.21 mmol/l after precipitation with heparin, dextran sulfate, and polyvinylsulfate, respectively. As compared to a combined ultracentrifugation and precipitation reference procedure (mean 3.22 mmol/l) two precipitation methods tend to underrate LDL-cholesterol. Elevated plasma triglycerides may interfere with the precipitation of LDL. The clinical relevance of the precipitation procedures has been studied by discriminant analysis in n = 28 consecutive patients admitted for coronary bypass operation and n = 28 controls. The data suggest that, statistically, the determination of LDL-cholesterol with either precipitation method only provides redundant information as in relation to the Friedewald approximation for LDL-cholesterol. Immunologically determined apolipoprotein B proved a better predictor for group separation than either precipitation method.

Analysis of plasma lipoproteins by ultracentrifugation in a new fixed angle rotor: evaluation of a phosphotungstic acid/MgCl2 precipitation and a quantitative lipoprotein electrophoresis assay

A routine procedure for the ultracentrifugal analysis of human plasma lipoproteins by means of a fixed angle rotor was developed. It was applied as reference method for the evaluation of two widely used procedures of lipoprotein analysis, i.e. measurement of HDL-cholesterol after precipitation of the apolipoprotein B containing lipoproteins with a new phosphotungstic acid/MgCl2 reagent, and a quantitative lipoprotein electrophoresis system. A new statistical approach to the multivariate comparison of analytical methods, the linear structural relationship model, has been applied. The HDL-cholesterol levels measured after phosphotungstic acid/MgCl2 precipitation agreed well to those determined by ultracentrifugation, whereas electrophoretically quantified alpha-lipoprotein-cholesterol exceeded the ultracentrifugal HDL-cholesterol. The Friedewald formula obviously underestimated LDL-cholesterol due to an overestimation of VLDL-cholesterol, whereas the electrophoretically quantified pre-beta- and beta-lipoprotein-cholesterol levels fairly coincided with the respective ultracentrifugal measurements. The inter-assay reproducibility of the HDL-cholesterol determination after phosphotungstic acid/MgCl2 precipitation and subsequent LDL-cholesterol quantification according to Friedewald was statistically equivalent to that of ultracentrifugation, whereas the quantitative lipoprotein electrophoresis proved less precise.