Daytime triglyceride variability in men and women with different levels of triglyceridemia

BACKGROUND

Triglyceride (TG) levels measured in either the fasting or non-fasting state predict the risk of cardiovascular disease (CVD). Since CVD risk assessment is affected by variability in TG, the aim of the study was to investigate intra-individual variability of non-fasting TG.

METHODS

Capillary triglyceride (cTG) levels were measured in 246 free-living individuals at six time-points during the day on three separate occasions. Intra-individual variability in cTG was assessed by calculating the standard deviation of three measures at each time-point. Subjects were analyzed by gender and by fasting TG level.

RESULTS

In the fasting state, intra-individual variability was similar in males and females (0.28 and 0.35 mmol/l, respectively), but increased significantly in male but not in female subjects during the day, i.e., 0.28 to 0.69, and 0.35 to 0.36 mmol/l, resp. Subjects with higher fasting TG levels had greater absolute variability in both fasting and non-fasting TG.

CONCLUSIONS

The variability in non-fasting TG is greater in males and in individuals with higher levels of TG. Since greatest variability in non-fasting TG occurs very late in the day, it is unlikely to affect the assessment of CVD risk, which is based on a blood sample taken during daylight hours.

Blood cholesterol concentration measured by CR3000: fingerstick versus venous sampling

Currently, the clinical practice of desktop or Point of Care (PoC) analyzers for lipid measurements has gained wide popularity. Designed to quickly perform measurements on microlitre(microL) quantities of blood, these instruments can be used in non-laboratory settings, such as physicians offices or field-testing sites and can provide measurements in whole blood, serum, or plasma, using either venous or capillary blood samples. The aim of this study is to examine the relationship between cholesterol determinations in venous and capillary samples using the CR3000 PoC system. The study was performed on 21 unselected adult volunteers, and no exclusion criteria was adopted. The mean cholesterol concentration for the venous blood samples measured was 164 mg/dL. The values obtained in the capillary blood samples averaged 168 mg/dL, which is only slightly higher (e.g., 2.87%) than the venous sample measurements. Moreover, the total variance was statistically similar for venous and capillary measurements (F value = 1.199, where the upper critical value of the F distribution is 2.124, p < 0.05). The results of our study support the concept that CR3000 total cholesterol testing can be performed safely and accurately in either venous or capillary specimens.

Multivariate Assessment of Lipid Parameters as Predictors of Coronary Heart Disease Among Postmenopausal Women

Background— Over the past decade, lipid measurements have been significantly improved and standardized. We evaluated the usefulness of multiple plasma lipid parameters in predicting coronary heart diseases (CHD) among women.

Methods and Results— Among 32 826 women from the Nurses’ Health Study who provided blood samples at baseline, 234 CHD events were documented during 8 years of follow-up. In a nested study, these cases were matched to controls (1:2) for age, smoking, fasting status, and month of blood draw. We estimated the relative risk (RR) for each lipid parameter, adjusted for C-reactive protein, homocysteine, body mass index, family history, hypertension, diabetes, postmenopausal hormone use, physical activity, alcohol intake, and blood draw parameters. The RRs associated with an increase of ≈1 SD (mg/dL) were as follows: HDL cholesterol (HDL-C) (RR=0.6 [0.5 to 0.8], SD=17), apolipoprotein B 100 (apoB 100 ) (RR=1.7 [1.4 to 2.1], SD=32), LDL cholesterol (LDL-C) (RR=1.4 [1.1 to 1.7], SD=36), total cholesterol (TC) (RR=1.4 [1.1 to 1.6], SD=40), and triglycerides (RR=1.3 [1.0 to 1.5], SD=80). Among the lipid indexes, the RRs were: apoB 100 /HDL-C (RR=1.7 [1.4 to 2.1], SD=1.0), TC/HDL-C (RR=1.6 [1.3 to 1.9], SD=1.3), LDL-C/HDL-C (RR=1.5 [1.3 to 1.9], SD=1.0), and non–HDL-C (RR=1.6 [1.3 to 1.9], SD=42 mg/dL). After simultaneous control for several lipid biomarkers, HDL-C was the primary contributor of the variation in multivariate models ( P =0.01), followed by LDL-C ( P =0.01), whereas triglycerides and apoB 100 did not contribute further information. HDL-C–related ratios were the strongest contributors to predicting CHD ( P <0.0001).

Conclusions— Lower levels of HDL-C may be a key discriminator of higher CHD events among postmenopausal women. HDL-C–related ratios (such as TC/HDL-C) provide a powerful predictive tool independently of other known CHD risk factors.

Intraindividual variability of children's blood lipid and lipoprotein concentrations: a review

Of the numerous risk factors that have been associated with atherosclerosis and subsequent coronary heart disease, none have caught the public's attention more than plasma cholesterol. An increasing number of studies are focusing on intervention strategies aimed at "improving" the plasma lipid-lipoprotein profile of children. However, the efficacy of these strategies cannot be ascertained unless the biologic and analytic variability of these metabolites has been determined. From the limited available literature, it would appear that the biologic variability of total cholesterol, high- and low-density lipoprotein cholesterol, and triacylglycerol in children is similar to that reported for adults. Yet studies that have directly focused on this important issue with children are scarce, especially those that have included a representative sample and measurements of lipoprotein subfractions. Further research is warranted with children to better establish the extent of intraindividual variation associated with the lipid-lipoprotein profile.

Circadian temporal organization of lipidic fractions in elderly people. Entrainment to the dietary schedule

BACKGROUND AND AIMS

Changes in some rhythmometric parameters have been reported in the elderly as a consequence of both structural and neurochemical changes occurring in the central nervous system. Since alterations of lipid and lipoprotein metabolism are directly involved in several age-related disorders, the aim of this study was to investigate the circadian temporal organization of some important lipidic fractions (total cholesterol, triacylglycerol, apolipoprotein A1 and B) in physiological aging.

METHODS

Thirty old hospitalized subjects were synchronized for daily activities, sleeping/waking habits, and time/quality of meals. Twenty-four healthy young individuals served as controls. After an overnight fast, samples were taken beginning at 08:00 every 4 hours until 20:00, and every 2 hours from 20:00 to 04:00. Rhythmometric data were analyzed by single and population mean Cosinor analysis, and by ANOVA; the comparison of the rhythm's parameters between elderly and young subjects was carried out by the Mesor test and the amplitude-acrophase using Hotelling's test.

RESULTS

Elderly subjects exhibited statistically significant circadian rhythms for total cholesterol (p<0.00002), triacylglycerol (p<0.000001), apo A-1 (p<0.0013), and apo B (p<O.0104). Young subjects also exhibited statistically significant daily fluctuations for total cholesterol (p<0. 0003), triacylglycerol (p<0. 03), apo A-1 (p<0.002) and apo B (p<0.003). The mean level of apo B rhythm was higher in old subjects than in controls.

CONCLUSIONS

These data suggest that the circadian temporal organization of lipidic fractions is maintained in physiological aging and underline the importance of the feeding schedule as a powerful synchronizer of the daily lipidic profile.

Postprandial lipemia and coronary risk

A number of cross-sectional studies have demonstrated that the magnitude of postprandial lipemia or single postprandial triglyceride values predict asymptomatic and symptomatic atherosclerosis, independent of risk factors measured in the fasting state. Postprandial lipemia reflects an integrated measure of an individual's triglyceride metabolic capacity. Numerous genetic and environmental factors that are known or suspected to affect triglyceride transport contribute to the magnitude of postprandial lipemia. In this article, mechanisms linking postprandial lipemia with the development and progression of atherosclerosis are described, and determinants of the extent and duration of postprandial lipemia are discussed.

Estimating the Long-Term Effects of Storage at −70 °C on Cholesterol, Triglyceride, and HDL-Cholesterol Measurements in Stored Sera

We estimated the effects of long-term storage at −70 °C on serum total cholesterol, HDL-cholesterol, and triglycerides in specimens that had been stored for up to 7 years. These estimates were made using measurements in serial specimens collected from the placebo control group of the Air Force/Texas Coronary Atherosclerosis Prevention Study over a period of ∼5 years. We compared the group means for pairs of serial specimens taken at 6- and 12-month intervals, assuming that (a) a negligible placebo effect occurred between the serial specimen pairs; (b) in the absence of storage effects, the variation in the group means would reflect only normal biological variation and would not materially affect the group means for the serial specimens; (c) any systematic changes in these group means would reflect storage-related changes; and (d) storage-related changes are cumulative, i.e., the overall changes for a given storage period are the sum of the changes during previous storage periods. We observed average decreases of 2.0% per year for total cholesterol over 7 years and 2.8% per year in triglycerides for the first 5 years. HDL-cholesterol decreased by 1.3% per year, but this change was not statistically significant. This approach may be useful for estimating storage-related changes for studies in specimens stored for a period of years and for which stability data may not be available.

Monthly intra-individual variation in lipids over a 1-year period in 22 normal subjects

OBJECTIVES

Previous reports on biological variation in lipids differ widely in the time interval between sampling, the number of samples analyzed per patient and the total study period. The present investigation was carried out to determine monthly intra-individual variation in lipids over 1 year and to establish whether there was a consistent change in lipid values over the summer months. The importance of taking this variation into consideration during the assessment of risk of coronary heart disease (CHD) was also examined.

DESIGN AND METHODS

Cholesterol, triglycerides, HDL, apo A1, and apo B were measured at monthly intervals for 12 months in 22 healthy, free-living volunteers (11 females, 11 males) by standardized methods.

RESULTS

When compared to analytical variation, biological variation was the dominant component of the intra-individual changes observed during the 1-year study period. As expected, triglycerides showed the greatest biological variation; the ratio of biological/analytical variation was 33.1. Much smaller ratios were observed for the other lipids measured in this study with values ranging from 4.2 to 6.8. Different subjects attained their maximum and minimum values in virtually every month of the year. There were significant reductions in cholesterol, HDL, LDL, and apo A1 in the summer months while triglycerides showed a non-significant increase and apo B a non-significant decrease during this period.

CONCLUSIONS

All the analytes showed considerable intra-individual variation. It is, therefore, important to measure lipids sequentially over several weeks to arrive at an average value for risk stratification for CHD.

Long-term variability of serum lipoprotein(a) concentrations in healthy fertile women

Lipoprotein(a) is a unique lipoprotein with atherothrombogenic properties. Although its blood concentration is mainly genetically determined, various factors exist which may cause variability. These may influence the clinical use of the results. We studied lipoprotein(a) biological variation by a rate nephelometric assay over a period of two years in a population of healthy fertile women. The study was performed in 12 volunteers, healthy subjects with various lipoprotein(a) concentrations, by monthly determinations during one year and a single determination one year later, together with measurements of total, high density lipoprotein and high density lipoprotein2 cholesterol, triglycerides and apolipoproteins A1 and B. The intra-individual variability of lipoprotein(a) ranged between 4 to 20%, with three subjects showing a coefficient of biological variation higher than 15%. In absolute terms, the difference between two determinations could represent 0.44 g/l or 50% of the mean value. This study suggests that physiological lipoprotein(a) variations should be taken into account for clinical purposes, especially in patients in need of thorough risk evaluation.

Magnetic resonance imaging-assessed adipose tissue and serum lipid and insulin concentrations in growth hormone-deficient adults. Effect of growth hormone replacement

The visceral and subcutaneous abdominal adipose tissue (AT) areas and the subcutaneous hip AT area were assessed by magnetic resonance imaging (MRI) in relation to serum lipid and plasma insulin levels in 12 growth hormone-deficient (GHD) adults before and after 6 months of replacement therapy with recombinant human growth hormone (rhGH) and in 12 healthy control subjects. Compared with control subjects, GHD patients had a significantly increased amount of visceral AT, which was inversely related with plasma HDL cholesterol and positively correlated with plasma triglyceride levels. Visceral AT was not associated with plasma total and LDL cholesterol or plasma insulin concentrations. GHD patients also had elevated serum total cholesterol, LDL cholesterol, and triglyceride levels compared with control subjects. After 6 months of rhGH replacement therapy the mean visceral, subcutaneous abdominal, and subcutaneous hip AT areas and serum concentration of total cholesterol decreased significantly, whereas serum HDL cholesterol concentration increased significantly. No significant correlations were found between changes in the amount of AT and changes in serum lipid and plasma insulin levels.

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.

Significance of various parameters derived from biological variability for lipid and lipoprotein analyses

Analytical, within-subject, and between-subject components of variability have been determined for total cholesterol, LDL-cholesterol, HDL-cholesterol, and its HDL2 and HDL3 subfractions, triglycerides, apolipoproteins A-I and B, and lipoprotein(a) in serum specimens from a cohort of 10 healthy subjects over a 1-month period. From these data, we have calculated the desirable analytical imprecisions, the indices of individuality, the critical differences for significant change detection, and the number of specimens required to estimate the homeostatic set-point of an individual. Practically, the analytical goal for imprecision was not achieved for HDL2 subfraction, lipoprotein(a), and direct LDL-cholesterol determination (obtained vs. theoretical analytical CV, 8.2% vs. 5.9%, 7.4% vs. 3.8%, and 3.2% vs. 2.6%, respectively). All analytes had marked individuality, showing that the use of population-based reference values is inadequate for their interpretation. The applicable differences required for two results to be significantly different (p < or = 0.05) are total cholesterol: 10%; triglycerides: 49%; LDL-cholesterol: 16%; HDL-cholesterol: 14%; HDL2-cholesterol: 40%; HDL3-cholesterol: 16%; apolipoprotein A-I: 11%; apolipoprotein B: 12%; and lipoprotein(a): 29%. Furthermore, it should be clear that population screening for the assessment of risk of coronary artery disease by means of some of the assays studied would result in a significant number of patients requiring analysis of multiple specimens.

Visceral fat loss measured by magnetic resonance imaging in relation to changes in serum lipid levels of obese men and women

The effect of weight reduction on serum lipids in relation to visceral fat accumulation was studied in 78 healthy obese subjects (40 premenopausal women and 38 men) aged 27-51 years and with an initial body mass index of 30.7 +/- 2.2 kg/m2 (mean +/- SD). The subjects received a 4.2 MJ/day energy-deficit diet for 13 weeks. Magnetic resonance imaging was used to assess abdominal fat areas before and after weight loss. Weight reductions of 12.6 +/- 3.2 kg in men and 11.7 +/- 3.8 kg in women resulted in larger reductions in the fasting serum levels of total cholesterol (p < 0.05), low density lipoprotein cholesterol (p = 0.06), and triglycerides (p < 0.01) and a larger increase in the high density lipoprotein cholesterol/low density lipoprotein cholesterol ratio (p = 0.05) in men compared with women. Men also lost more visceral fat (p < 0.0001), whereas the reductions in the total and subcutaneous abdominal fat depots were similar. In women, visceral fat loss was significantly related with an increase of the high density lipoprotein cholesterol level, independent of the degree of total fat loss. In men, however, no significant correlations were observed between changes in visceral fat and any of the serum lipids. Comparisons of average changes in obese men and women suggest that visceral fat loss is associated with an improvement of the serum lipid profile. However, correlation analysis does not support a critical role of visceral fat in determining serum lipid concentrations on an individual level, except for an improvement of the high density lipoprotein cholesterol level with visceral fat loss in obese women.

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.