Altered properties of high density lipoprotein subfractions in obese subjects

Effects of the DailyColors™ polyphenol supplement on serum proteome, cognitive function, and health in older adults at risk of cognitive and functional decline

The Mediterranean diet is associated with reduced mortality and cognitive decline, largely due to its polyphenol content. However, Western populations often do not meet recommended fruit and vegetable intakes. Polyphenols exert anti-inflammatory effects and may influence extracellular vesicle (EV) dynamics. DailyColors™ is a polyphenol-rich blend inspired by this dietary pattern, containing extracts from 16 fruits, vegetables, and herbs. This 60-day, double-blind, placebo-controlled, randomised trial involved 150 UK adults aged 50+ with a BMI ≥ 25, recruited to complete cognitive and physical fitness assessments via the PROTECT-UK online platform. Participants received either a medium (750 mg) or high (2000 mg) dose of DailyColors™ (∼300 mg and ∼750 mg polyphenols, respectively) or a placebo. A sub-group (n = 15 per group) underwent additional assessments, including blood pressure measurements, characterisation of circulating EVs and tandem-mass-tagged serum proteomics. Significant cognitive benefits were observed, with improvements in reaction time for the high-dose group and accuracy for both active supplement groups. The high-dose group also showed significant physical fitness gains on the Timed Stand test (P < 0.001). All groups significantly improved on the Chair Stand test. Proteomic analysis showed significantly reduced serum protein expression in immune and pre-β1-HDL pathways, suggesting anti-inflammatory effects. Pre-β1-HDL proteins are typically elevated in obesity; their reduction suggests a reversal of this effect. No significant changes were noted in EV concentration or size. DailyColors™ supplementation, may enhance cognitive function, physical fitness, and systemic health in older, overweight adults. These findings warrant further investigation in larger trials.

Sex differences in the associations of HDL particle concentration and cholesterol efflux capacity with incident coronary artery disease in type 1 diabetes: The RETRO HDLc cohort study

BACKGROUND

In type 1 diabetes, women lose their relative protection (compared to men) against coronary artery disease (CAD), while high-density lipoprotein cholesterol (HDL-C) is less strongly associated with lower CAD risk in women.

OBJECTIVE

We aimed to assess whether sex differences in the HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) association with CAD may explain these findings.

METHODS

HDL-P (calibrated differential ion mobility analysis) and total and ATP binding cassette transporter A1 (ABCA1)-specific CEC were quantified among 279 men and 271 women with type 1 diabetes (baseline mean age 27·8 years; diabetes duration, 19·6 years). Clinical CAD was defined as CAD death, myocardial infarction and/or coronary revascularization.

RESULTS

Women had higher large HDL-P levels and marginally lower concentrations of small HDL-P and ABCA1-specific CEC than men. No sex differences were observed in extra-small HDL-P, medium HDL-P and total CEC. During a median follow-up of 26 years, 37·6 % of men and 35·8 % of women developed CAD (p = 0·72). In multivariable Cox models stratified by sex (pTotal HDL-P x sex interaction=0·01), HDL-P was negatively associated with CAD incidence in both sexes. However, associations were stronger in men, particularly for extra-small HDL-P (hazard ratio (HR)men=0·11, 95 % confidence interval (CI): 0·04-0·30; HRwomen=0·68, 95 % CI: 0·28-1·66; pinteraction=0·001). CEC did not independently predict CAD in either sex.

CONCLUSION

Despite few absolute differences in HDL-P concentrations by sex, the HDL-P - CAD association was weaker in women, particularly for extra-small HDL-P, suggesting that HDL-P may be less efficient in providing atheroprotection in women and perhaps explaining the lack of a sex difference in CAD in type 1 diabetes.

Obesity Affects Maternal and Neonatal HDL Metabolism and Function

Pregravid obesity is one of the major risk factors for pregnancy complications such as gestational diabetes mellitus (GDM) and an increased risk of cardiovascular events in children of affected mothers. However, the biological mechanisms that underpin these adverse outcomes are not well understood. High-density lipoproteins (HDLs) are antiatherogenic by promoting the efflux of cholesterol from macrophages and by suppression of inflammation. Functional impairment of HDLs in obese and GDM-complicated pregnancies may have long-term effects on maternal and offspring health. In the present study, we assessed metrics of HDL function in sera of pregnant women with overweight/obesity of the DALI lifestyle trial (prepregnancy BMI ≥ 29 kg/m2) and women with normal weight (prepregnancy BMI < 25 kg/m2), as well as HDL functionalities in cord blood at delivery. We observed that pregravid obesity was associated with impaired serum antioxidative capacity and lecithin−cholesterol acyltransferase activity in both mothers and offspring, whereas maternal HDL cholesterol efflux capacity was increased. Interestingly, functionalities of maternal and fetal HDL correlated robustly. GDM did not significantly further alter the parameters of HDL function and metabolism in women with obesity, so obesity itself appears to have a major impact on HDL functionality in mothers and their offspring.

HDL Composition, Heart Failure, and Its Comorbidities

Although research on high-density lipoprotein (HDL) has historically focused on atherosclerotic coronary disease, there exists untapped potential of HDL biology for the treatment of heart failure. Anti-oxidant, anti-inflammatory, and endothelial protective properties of HDL could impact heart failure pathogenesis. HDL-associated proteins such as apolipoprotein A-I and M may have significant therapeutic effects on the myocardium, in part by modulating signal transduction pathways and sphingosine-1-phosphate biology. Furthermore, because heart failure is a complex syndrome characterized by multiple comorbidities, there are complex interactions between heart failure, its comorbidities, and lipoprotein homeostatic mechanisms. In this review, we will discuss the effects of heart failure and associated comorbidities on HDL, explore potential cardioprotective properties of HDL, and review novel HDL therapeutic targets in heart failure.

BMI modifies the association between serum HDL cholesterol and stroke in a hypertensive population without atrial fibrillation

PURPOSE

Both high-density lipoprotein cholesterol (HDL-C) and body mass index (BMI) have an impact on the prevalence of stroke. However, it is unclear whether BMI can modify the relationship between HDL-C and stroke. Therefore, we aimed to assess the effect of the BMI on the association between HDL-C and stroke in a hypertensive population without atrial fibrillation (AF).

METHODS

We analyzed data of 10,925 hypertensive patients without AF from the Chinese Hypertension Registry Study. BMI was categorized as < 24 and ≥ 24 kg/m². Multivariate logistic regression and smooth curve fitting (penalized spline method) were used to analyze the association between HDL-C and stroke in different BMI groups. Subgroup analysis and interaction tests were used to explore the effect of other variables on this relationship.

RESULTS

The results showed a negative association between HDL-C and stroke in the BMI < 24 kg/m² group, but HDL-C was not associated with stroke in the BMI ≥ 24 kg/m² group. In the BMI < 24 kg/m² group, each 1 mmol/L increase in HDL-C was associated with a 50% decreased risk of stroke [odds ratio (OR) 0.50, 95% confidence interval (CI) 0.38-0.66]. No significant relationship between HDL-C and stroke was observed in the BMI ≥ 24 kg/m² group (OR 0.73, 95% CI 0.49-1.10). There was a significant interaction between BMI and HDL-C in regard to the prevalence of stroke in the hypertensive population without AF (P_Interaction = 0.027).

CONCLUSIONS

We found an inverse association between HDL-C and stroke only in the BMI < 24 kg/m² group. The finding suggested that BMI could modify the association between HDL-C and stroke in hypertensive populations without AF.

Interaction between adipocytes and high-density lipoprotein:new insights into the mechanism of obesity-induced dyslipidemia and atherosclerosis

Obesity is the most common nutritional disorder worldwide and is associated with dyslipidemia and atherosclerotic cardiovascular disease. The hallmark of dyslipidemia in obesity is low high density lipoprotein (HDL) cholesterol (HDL-C) levels. Moreover, the quality of HDL is also changed in the obese setting. However, there are still some disputes on the explanations for this phenomenon. There is increasing evidence that adipose tissue, as an energy storage tissue, participates in several metabolism activities, such as hormone secretion and cholesterol efflux. It can influence overall reverse cholesterol transport and plasma HDL-C level. In obesity individuals, the changes in morphology and function of adipose tissue affect plasma HDL-C levels and HDL function, thus, adipose tissue should be the main target for the treatment of HDL metabolism in obesity. In this review, we will summarize the cross-talk between adipocytes and HDL related to cardiovascular disease and focus on the new insights of the potential mechanism underlying obesity and HDL dysfunction.

Effects of weight change on HDL-cholesterol and its subfractions in over 28,000 men and women

BACKGROUND

Changes in body mass index (ΔBMI) have well-established relationships to changes in high-density lipoprotein (ΔHDL)-cholesterol concentrations; however, their relationships to ΔHDL subfractions are less well understood.

OBJECTIVE

Assess the associations between ΔHDL and ΔBMI in a very large cohort.

METHOD

Age and sex-adjusted Δapo A1 concentrations were measured within 10 HDL subfractions in 14,121 women and 13,969 men using two-dimensional HDL-mapping. Significance was identified at .01 < P ≤ .05 (*), .001 < P ≤ .01 (†), .0001 < P ≤ .001 (‡), and P ≤ .0001 (§).

RESULTS

ΔBMI was significantly associated with Δα-1 (very large HDL, slope ± SE, females: -0.39 ± 0.07^§; males: -0.51 ± 0.05^§), Δα-3 (medium HDL, females: 0.18 ± 0.04^§; males: 0.19 ± 0.04^§), and Δα-4 (small HDL, females: 0.14 ± 0.03^§; males: 0.15 ± 0.04^§ mg/dL per kg/m²). As a percent of baseline, the changes in α-1 per ΔBMI were nearly twice as great as the changes in HDL-cholesterol per ΔBMI in both males (-1.53% vs -0.77%) and females (-0.79% vs -0.42%). HDL-cholesterol decreased significantly in healthy-weight patients who became overweight, overweight patients who became class I or class II obese, class I obese patients who became class II obese, and class II obese patients who became class III. In contrast, HDL-cholesterol increased in class III obese patients who became class II or class I, class II obese patients who became class I or overweight, class I patients who became overweight or healthy weight, overweight patients who became healthy weight, and healthy weight patients who became underweight.

CONCLUSIONS

Weight change significantly affects HDL-cholesterol concentrations throughout the obesity spectrum. ΔBMI's effect on Δα-1 was nearly twice as great as its effect on HDL-cholesterol.

APOL1 nephropathy risk variants are associated with altered high-density lipoprotein profiles in African Americans

BACKGROUND

Two independent coding variants in the apolipoprotein L1 gene (APOL1), G1 and G2, strongly associate with nephropathy in African Americans; associations with cardiovascular disease are more controversial. Although APOL1 binds plasma high-density lipoproteins (HDLs), data on APOL1 risk variant associations with HDL subfractions are sparse.

METHODS

Two APOL1 G1 single nucleotide polymorphisms and the G2 insertion/deletion polymorphism were genotyped in 2010 Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study participants with nuclear magnetic resonance spectroscopy-based lipoprotein subfraction measurements. Linear regression was used to model associations between numbers of APOL1 G1/G2 risk variants and HDL subfractions, adjusting for demographic, clinical and ancestral covariates.

RESULTS

Female sex and higher percentage of African ancestry were positively associated with the number of APOL1 G1/G2 risk alleles. In the unadjusted analysis, mean (standard error) small HDL concentrations (μmol/L) for participants with zero, one and two G1/G2 risk alleles were 19.0 (0.2), 19.7 (0.2) and 19.9 (0.4), respectively (P = 0.02). Adjustment for age, sex, diabetes and African ancestry did not change the results but strengthened the statistical significance (P = 0.004). No significant differences in large or medium HDL, very low-density lipoprotein or low-density lipoprotein particle concentrations were observed by APOL1 genotype.

CONCLUSIONS

Greater numbers of APOL1 G1/G2 risk alleles were associated with higher small HDL particle concentrations in African Americans. These results may suggest novel areas of investigation to uncover reasons for the association between APOL1 risk variants with adverse outcomes in African Americans.

Obesity favors apolipoprotein E- and C-III-containing high density lipoprotein subfractions associated with risk of heart disease

Human HDLs have highly heterogeneous composition. Plasma concentrations of HDL with apoC-III and of apoE in HDL predict higher incidence of coronary heart disease (CHD). The concentrations of HDL-apoA-I containing apoE, apoC-III, or both and their distribution across HDL sizes are unknown. We studied 20 normal weight and 20 obese subjects matched by age, gender, and race. Plasma HDL was separated by sequential immunoaffinity chromatography (anti-apoA-I, anti-apoC-III, anti-apoE), followed by nondenaturing-gel electrophoresis. Mean HDL-cholesterol concentrations in normal weight and obese subjects were 65 and 50 mg/dl (P = 0.009), and total apoA-I concentrations were 119 and 118 mg/dl, respectively. HDL without apoE or apoC-III was the most prevalent HDL type representing 89% of apoA-I concentration in normal weight and 77% in obese (P = 0.01) individuals; HDL with apoE-only was 5% versus 8% (P = 0.1); HDL with apoC-III-only was 4% versus 10% (P = 0.009); and HDL with apoE and apoC-III was 1.5% versus 4.6% (P = 0.004). Concentrations of apoE and apoC-III in HDL were 1.5-2× higher in obese subjects (P ≤ 0.004). HDL with apoE or apoC-III occurred in all sizes among groups. Obese subjects had higher prevalence of HDL containing apoE or apoC-III, subfractions associated with CHD, whereas normal weight subjects had higher prevalence of HDL without apoE or apoC-III, subfractions with protective association against CHD.

High-density lipoprotein metabolism in human apolipoprotein B(100) transgenic/brown adipose tissue deficient mice: a model of obesity-induced hyperinsulinemia

Obese and diabetic humans display decreased plasma high-density lipoprotein cholesterol (HDL-C) concentrations and an increased risk for coronary heart disease. However, investigation on HDL metabolism in obesity with a particular emphasis on hepatic ATP-binding cassette transporter A1 (ABCA1), the primary factor for HDL formation, has not been well studied. Human apolipoprotein B(100) transgenic (hApoB(tg)) and brown adipose tissue deficient (BATless) mice were crossed to generate hApoB(tg)/BATless mice. Male and female hApoB(tg) and hApoB(tg)/BATless mice were maintained on either a regular rodent chow diet or a diet high in fat and cholesterol until 24 weeks of age. The hApoB(tg)/BATless mice that were fed a HF/HC diet became obese, developed hepatic steatosis, and had significantly elevated plasma insulin levels compared with their hApoB(tg) counterparts, but plasma concentrations of total cholesterol, HDL-C, triglycerides, and free fatty acids and lipoprotein distribution between genotypes were not significantly different. Hepatic expression of genes encoding HDL-modifying factors (e.g., scavenger receptor, class B, type I, hepatic lipase, lecithin:cholesterol acyltransferase, and phospholipid transfer protein) was either altered significantly or showed a trend of difference between 2 genotypes of mice. Importantly, hepatic protein levels of ABCA1 were significantly lowered by ∼35% in male obese hApoB(tg)/BATless mice with no difference in mRNA levels compared with hApoB(tg) counterparts. Despite reduced hepatic ABCA1 protein levels, plasma HDL-C concentrations were not altered in male obese hApoB(tg)/BATless mice. The result suggests that hepatic ABCA1 may not be a primary contributing factor for perturbations in HDL metabolism in obesity-induced hyperinsulinemia.

High pre-beta1 HDL concentrations and low lecithin: cholesterol acyltransferase activities are strong positive risk markers for ischemic heart disease and independent of HDL-cholesterol

BACKGROUND

We hypothesized that patients with high HDL-cholesterol (HDL-C) and ischemic heart disease (IHD) may have dysfunctional HDL or unrecognized nonconventional risk factors.

METHODS

Individuals with IHD (Copenhagen University Hospital) and either high HDL-C (n = 53; women >or=735 mg/L; men >or=619 mg/L) or low HDL-C (n = 42; women

RESULTS

Pre-beta(1) HDL concentrations were 2-fold higher in individuals with IHD vs no IHD in both the high [63 (5.7) vs 35 (2.3) mg/L; P < 0.0001] and low HDL-C [49 (5.0) vs 27 (1.5) mg/L; P = 0.001] groups. Low LCAT activity was also associated with IHD in the high [95.2 (6.7) vs 123.0 (5.3) micromol x L(-1) x h(-1); P = 0.002] and low [93.4 (8.3) vs 113.5 (4.9) micromol x L(-1) . h(-1); P = 0.03] HDL-C groups. ROC curves for pre-beta(1) HDL in the high-HDL-C groups yielded an area under the curve of 0.71 (95% CI: 0.61-0.81) for predicting IHD, which increased to 0.92 (0.87-0.97) when LCAT was included. Similar results were obtained for low HDL-C groups. An inverse correlation between LCAT activity and pre-beta(1) HDL was observed (r(2) = 0.30; P < 0.0001) in IHD participants, which was stronger in the low HDL-C group (r(2) = 0.56; P < 0.0001).

CONCLUSIONS

IHD was associated with high pre-beta(1) HDL concentrations and low LCAT levels, yielding correct classification in more than 90% of the IHD cases for which both were measured, thus making pre-beta(1) HDL concentration and LCAT activity level potentially useful diagnostic markers for cardiovascular disease.

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MESH Headings

• Biomarkers/blood
• Cholesterol, HDL/blood
• Female
• High-Density Lipoproteins, Pre-beta/blood
• Humans
• Lecithins/blood
• Male
• Middle Aged
• Myocardial Ischemia/blood
• Myocardial Ischemia/diagnosis
• Risk Factors
• Sterol O-Acyltransferase/blood

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Grants

• Z99 HL999999 Intramural NIH HHS

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Affiliation(s)

Amar A Sethi NIH, National Heart Lung and Blood Institute, Lipoprotein Metabolism Section, Bethesda, MD, USA.
Maureen Sampson
Russell Warnick
Nehemias Muniz
Boris Vaisman
Børge G Nordestgaard
Anne Tybjaerg-Hansen
Alan T Remaley

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Collaborators Collapse

HDL-paraoxonase and membrane lipid peroxidation: a comparison between healthy and obese subjects

High-density lipoproteins (HDLs) play a key role in the protection against oxidative damage. The enzyme paraoxonase-1 (PON1) associated at the surface of HDL modulates the antioxidant and anti-inflammatory role of HDL. Previous studies have demonstrated a decrease of serum PON in obese patients. The aim of this study was to investigate whether modifications of PON1 activity reflect in a different ability to protect and/or repair biological membranes against oxidative damage. Thirty obese patients at different grades of obesity (BMI ranging from 30.4 to 64.0 kg/m(2)) and 62 age-matched control subjects (BMI <25 kg/m(2)) were included in the study. The ability of HDL to protect membranes against oxidative damage was studied using erythrocyte membranes oxidized with 2,2-azobis(2 amidinopropane)dihydrochloride (AAPH) (ox-membrane). The membrane lipid hydroperoxide levels were evaluated after the incubation of ox-membranes in the absence or in the presence of HDL of controls or obese patients. The results confirm that HDL exerts a protective effect against lipid peroxidation. The ability of HDL to repair erythrocyte membranes was positively correlated with HDL-PON activity and negatively correlated with lipid hydroperoxide levels in HDL. These results suggest that PON modulates the HDL repairing ability. HDL from obese patients repaired less efficiently erythrocyte membranes against oxidative damage with respect to HDL from healthy subjects. A negative relationship has been established between BMI of obese patients and the protective effect of HDL. In conclusion, the decrease of HDL-PON activity and the lower HDL protective action against membrane peroxidation in obese patients could contribute to accelerate the cellular oxidative damage and arteriosclerosis in obesity.

Plasma triglyceride levels and body mass index values are the most important determinants of prebeta-1 HDL concentrations in patients with various types of primary dyslipidemia

OBJECTIVE

Experimental studies have shown that the prebeta-1 subclass of high-density lipoprotein particles (prebeta-1 HDL) may play an important role in the reverse cholesterol transport pathway as the initial acceptors of cellular cholesterol. The aim of the present study was the direct comparison of prebeta-1 HDL values in individuals with various types of primary dyslipidemias.

METHODS

Four hundred and eighty-six unrelated individuals were included in the study. According to their lipid values study participants were subdivided into four groups: control group (n=206), type IIA dyslipidemia group (n=148), type IIB dyslipidemia group (n=49) and type IV dyslipidemia group (n=83).

RESULTS

All dyslipidemic patients displayed higher concentrations of prebeta-1 HDL compared to control individuals. However, patients with dyslipidemias characterized by an abnormal catabolism of triglyceride-rich lipoproteins (such as dyslipidemias of type IIB and IV) tend to have higher prebeta-1 HDL values compared to patients with hypercholesterolemia, and this increase is proportional to the degree of hypertriglyceridemia. In addition, patients with metabolic syndrome exhibited significantly higher levels of prebeta-1 HDL compared to individuals that do not fulfill the criteria for the diagnosis of this syndrome. Multiple regression analysis revealed that serum triglyceride concentrations and body mass index (BMI) values were the most important determinants of prebeta-1 HDL levels in our population.

CONCLUSION

All dyslipidemic patients exhibit increased prebeta-1 HDL concentrations as compared to normolipidemic individuals. Whether this increase represents a defensive mechanism against atherosclerosis or it is indicative of impaired maturation of HDL particles and thus of a defective reverse cholesterol transport mechanism remains to be established.

Interactions between lipoproteins and platelet membranes in obesity

The aim was to investigate low-density lipoprotein (LDL) composition and Na(+)/K(+) adenosine triphosphatase (ATPase) and Ca(2+) ATPase activities and membrane fluidity measured by 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) in platelets from obese patients and controls in order to identify, if any, platelet membrane's chemical-physical and/or functional modifications associated with compositional modification of circulating lipoproteins. Moreover, we studied the in vitro effect on both platelet transmembrane cationic transport and fluidity, by incubating LDL from 30 obese subjects with platelets from 30 control subjects. The analysis of the chemical composition of LDL from obese patients showed a significant increase in the percent content of total cholesterol (TC) and triglycerides (TGs) and in the mean levels of lipid hydroperoxides compared to controls' LDL. Platelet Na(+)/K(+) ATPase and Ca(2+) ATPase activities showed, respectively, a significant decrease and increase in patients compared to controls; minor significant, respectively, decreases and increases are shown also in control platelets incubated with LDL from obese patients. Anisotropy tested with TMA-DPH probe was significantly increased both in platelets from obese patients and in control platelets incubated with LDL from obese patients compared to control platelets. This study highlights that obesity induces remarkable modifications both in lipoproteins and platelets. Both platelet hyperfunction and quantitative/qualitative alterations in plasma lipoproteins, as well as an altered interaction between circulating lipoproteins and platelets, might play a relevant role in the increased prevalence of the early atherosclerotic lesions development in obese subjects. The present data point out that obesity might represent a major potentially modifiable risk factor for the onset of numerous complications, in particular cardiovascular ones.

Plasma pre beta1-HDL level is elevated in unstable angina pectoris

Pre beta1-HDL, a minor HDL subfraction consisting of apolipoprotein A-I (apoA-I), phospholipids and unesterified cholesterol, plays an important role in reverse cholesterol transport. Plasma pre beta1-HDL levels have been reported to be increased in patients with coronary artery disease (CAD) and dyslipidemia. To clarify the clinical significance of measuring plasma pre beta1-HDL levels, we examined those levels in 112 patients with CAD, consisting of 76 patients with stable CAD (sCAD) and 36 patients with unstable angina pectoris (uAP), and in 30 patients without CAD as controls. The pre beta1-HDL levels were determined by immunoassay using a specific monoclonal antibody (Mab55201) that we established earlier. The mean pre beta1-HDL level in the CAD patients was significantly higher than the level in the controls (34.8+/-12.9 mg/L vs. 26.6+/-6.9 mg/L, p<0.001). In addition, the mean pre beta1-HDL level was markedly higher in the uAP subgroup than in the sCAD subgroup (43.1+/-11.5mg/L vs. 30.9+/-11.7 mg/L, p<0.0001). These tendencies remained even after excluding dyslipidemic subjects. These results suggest that elevation of the plasma pre beta1-HDL level is associated with the atherosclerotic phase of CAD and may be useful for identifying patients with uAP.

Effect of obesity on high-density lipoprotein metabolism

Reduced levels of high-density lipoproteins (HDL) in non-obese and obese states are associated with increased risk for the development of coronary artery disease. Therefore, it is imperative to determine the mechanisms responsible for reduced HDL in obese states and, conversely, to examine therapies aimed at increasing HDL levels in these individuals. This paper examines the multiple causes for reduced HDL in obese states and the effect of exercise and diet--two non-pharmacologic therapies--on HDL metabolism in humans. In general, the concentration of HDL-cholesterol is adversely altered in obesity, with HDL-cholesterol levels associated with both the degree and distribution of obesity. More specifically, intra-abdominal visceral fat deposition is an important negative correlate of HDL-cholesterol. The specific subfractions of HDL that are altered in obese states include the HDL2, apolipoprotein A-I, and pre-beta1 subfractions. Decreased HDL levels in obesity have been attributed to both an enhancement in the uptake of HDL2 by adipocytes and an increase in the catabolism of apolipoprotein A-I on HDL particles. In addition, there is a decrease in the conversion of the pre-beta1 subfraction, the initial acceptor of cholesterol from peripheral cells, to pre-beta2 particles. Conversely, as a means of reversing the decrease in HDL levels in obesity, sustained weight loss is an effective method. More specifically, weight loss achieved through exercise is more effective at raising HDL levels than dieting. Exercise mediates positive effects on HDL levels at least partly through changes in enzymes of HDL metabolism. Increased lipid transfer to HDL by lipoprotein lipase and reduced HDL clearance by hepatic triglyceride lipase as a result of endurance training are two important mechanisms for increases in HDL observed from exercise.

Indices of reverse cholesterol transport in subjects with metabolic syndrome after treatment with rosuvastatin

OBJECTIVE

The effects of the statin, rosuvastatin on indices of reverse cholesterol transport were studied in a randomized, placebo-controlled, cross-over trial in 25 overweight subjects with defined metabolic syndrome.

RESULT

Four weeks' treatment with 40 mg/day rosuvastatin significantly reduced levels of plasma cholesterol (44%), LDL cholesterol (60%) and triglyceride (38%). HDL cholesterol (mean [S.D.]) rose (0.97[0.17] to 1.05[0.17]mmol/L; P<0.05) and the LpA-I component of HDL from 39[7] to 45[9]mg/dL (P<0.05). LCAT activity fell (0.55[0.13] to 0.35[0.07]nmol/mL/h; P<0.05); CETP activity and mass fell from 89[13] to 80[11]nmol//L/h and from 1.66[0.57] to 1.28[0.41]mug/mL respectively, (P<0.05). Cholesterol efflux in vitro (to plasmas from THP-1 activated cells) fell from 7.1[1.8]% (placebo) to 6.2[1.7]% (rosuvastatin); P<0.05, but when plasmas depleted of apoB lipoproteins were studied, the difference in efflux was no longer statistically significant. During placebo efflux was paradoxically inversely correlated with HDL-C (P=0.016) and LpA-I (P=0.035) concentrations but these correlations were absent after rosuvastatin.

CONCLUSIONS

The data suggest possible HDL dysfunctionality in subjects with metabolic syndrome. The reduced capacity of plasmas following statin treatment to stimulate cholesterol efflux in vitro occurred in association with reduction in apoB lipoproteins and reduced activities of CETP and LCAT, and despite increased levels of HDL cholesterol.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Kinetics of prebeta1 HDL and alphaHDL in type II diabetic patients

BACKGROUND

The aim of this study was to analyze the recycling of high density lipoprotein (HDL) in six type II diabetic patients compared with six control subjects by endogenous labelling of apolipoprotein A-I (Apo A-I) with stable isotope Apo A.

MATERIALS AND METHODS

The -I-HDL kinetics were performed by infusion of (5.5.5-(2)H3)-leucine for 14 h. The prebeta1 and alphaHDL were separated by gel filtration fast protein liquid chromatrography system (FPLC). Kinetics of isotopic enrichment of Apo A-I were analyzed with a multi-compartmental model software (SAAM II, SAAM Institute, Seattle, WA).

RESULTS

Plasma Apo A-I concentration was decreased in patients with type II diabetes as a result of a decrease in Apo A-I-alphaHDL (P < 0.05). Diabetic patients were also characterized by an increased relative contribution of Apo A-I in prebeta1 HDL (18.3 +/- 2.8% vs 11.9 +/- 3.7%, P < 0.01). The synthetic rate of prebeta1 HDL was slightly increased in diabetic patients compared with control (NS) and an increase of recycling rate of alpha to prebeta1 HDL was observed (11.67 +/- 3.14 d(-1) vs 7.09 +/- 4.51 d(-1), P < 0.05). The clearance rate of Apo A-I was higher in diabetic patients (P < 0.05 for Apo A-I-prebeta1 HDL and P < 0.005 for Apo A-I-alphaHDL).

CONCLUSION

This study suggests that the usual increase in prebeta1 HDL in type II diabetic patients is mainly related to an increased conversion rate of alpha to prebeta1 HDL.

Apolipoprotein A-I, B-100, and B-48 metabolism in subjects with chronic kidney disease, obesity, and the metabolic syndrome

The metabolism of apolipoproteins (apo)B-48, B-100, and A-I was studied with a primed constant infusion of deuterium-labeled leucine in the fed state in 3 male individuals with chronic kidney disease (CKD), a glomerular filtration rate (GFR) of 28 to 57 mL/min/1.73 m2, obesity (body mass index [BMI] 33.1), and the metabolic syndrome. Compared to 5 obese controls (BMI 30.1) and 13 non-obese controls (BMI 25.2), these CKD subjects had high plasma levels of triglycerides (TG) (343 +/- 27.5 mg/dL v 144 +/- 34.4 in the obese controls, P < .001) and low apoA-I (86.7 +/- 3.9 mg/dL). An abnormal high-density lipoprotein (HDL) particle subpopulation pattern was found, with low levels of pre beta-1 and alpha1. Compared to the obese controls, very-low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) apoB-100 levels were elevated 2- to 3-fold, while LDL apoB-100 levels were slightly lower (-7 %) and apoB-48 levels were comparable. The high TG levels were not associated with statistically significant changes in VLDL apoB-100 kinetics, although the production rate (PR) was higher and the fractional catabolic rate (FCR) was lower. The slightly lower LDL apoB-100 levels were accompanied by a significant 3-fold increase in the FCR and a 2.7-fold increase in the PR. The lower apoA-I levels were accompanied by a 1.6-fold increase in the FCR. Compared to the non-obese controls, the PR of apoA-I was increased by 61% and 38%, respectively (P < .001) in CKD and in obese control subjects. In the control subjects, the PR of apoA-I was significantly correlated with the BMI (r = 0.81, P < .0001). The kinetic results are consistent with these hypotheses: (1) CKD is associated with decreased clearance of the TG-rich lipoproteins (TRLs) and increased catabolism of LDL; (2) obesity increases apoB-100 and apoA-I production; and (3) in CKD, TG transfer to HDL, making HDL more susceptible to catabolism, accounts for the low apoA-I levels.

Physical Fitness and Reverse Cholesterol Transport

BACKGROUND

Physical exercise is associated with a decreased risk of cardiovascular disease, which may be partly caused by the effect of exercise on the lipoprotein profile. The most consistent effect of exercise on lipoprotein metabolism is an increase in high-density lipoprotein (HDL).

METHODS AND RESULTS

Parameters of reverse cholesterol transport (RCT) in 25 endurance-trained male athletes were compared with 33 age-matched males enjoying an active lifestyle. VO2max was higher in athletes than in controls (53.4+/-1.2 versus 38.8+/-1.0 mL/min per kg; P<0.01). The following differences in parameters of RCT were found: (1) plasma HDL cholesterol and apoA-I levels were higher in athletes compared with controls (1.7+/-0.1 versus 1.4+/-0.1 mmol/L; P<0.001; and 145+/-2 versus 128+/-3 mg/dL; P<0.001, respectively). Both correlated with VO2max up to the value of 51 mL/min per kg; (2) prebeta1-HDL was higher in athletes than in controls (54+/-4 versus 37+/-3 microg/mL; P<0.001) and correlated positively with VO2max; (3) lecithin cholesterol: acyltransferase activity was higher in athletes (29.8+/-1.2 versus 24.2+/-1.4 nmol/microL per hour; P<0.005); and (4) the capacity of plasma to promote cholesterol efflux from macrophages was higher in athletes (18.8%+/-0.8% versus 16.2%+/-0.3%; P<0.03).

CONCLUSIONS

The likely reason for higher HDL concentration in physically fit people is increased formation of HDL from apoA-I and cellular lipids.

Prebeta high density lipoprotein has two metabolic fates in human apolipoprotein A-I transgenic mice

We compared the in vivo metabolism of prebeta HDL particles isolated by anti-human apolipoprotein A-I (apoA-I) immunoaffinity chromatography (LpA-I) in human apoA-I transgenic (hA-I Tg) mice with that of lipid-free apoA-I (LFA-I) and small LpA-I. After injection, prebeta LpA-I were removed from plasma more rapidly than were LFA-I and small LpA-I. Prebeta LpA-I and LFA-I were preferentially degraded by kidney compared with liver; small LpA-I were preferentially degraded by the liver. Five minutes after tracer injection, 99% of LFA-I in plasma was found to be associated with medium-sized (8.6 nm) HDL, whereas only 37% of prebeta tracer remodeled to medium-sized HDL. Injection of prebeta LpA-I doses into C57Bl/6 recipients resulted in a slower plasma decay compared with hA-I Tg recipients and a greater proportion (>60%) of the prebeta radiolabel that was associated with medium-sized HDL. Prebeta LpA-I contained one to four molecules of phosphatidylcholine per molecule of apoA-I, whereas LFA-I contained less than one. We conclude that prebeta LpA-I has two metabolic fates in vivo, rapid removal from plasma and catabolism by kidney or remodeling to medium-sized HDL, which we hypothesize is determined by the amount of lipid associated with the prebeta particle and the particle's ability to bind to medium-sized HDL.

Alterations of HDL subclasses in hyperlipidemia

BACKGROUND

It is generally accepted that different high-density lipoprotein (HDL) subclasses have distinct but interrelated metabolic functions. HDL is known to directly influence the atherogenic process and changes in HDL subclasses distribution may be related to the incidence and prevalence of atherosclerosis.

METHOD

The relative apolipoprotein (apo)A-I contents (% apoA-I) of plasma HDL subclasses were determined by two-dimensional gel electrophoresis coupled with immunodetection for apoA-I, in 39 hypercholesterolemic (HTC) subjects, 97 hypertriglyceridemic (HTG) subjects and 32 mixed hyperlipidemic (MHL) subjects, and 124 normolipidemic subjects.

RESULTS

The relative apoA-I contents of prebeta(1)-HDL, prebeta(2)-HDL, HDL(3c), HDL(3b) and HDL(3a) significantly increased while HDL(2a) and HDL(2b) significantly decreased in hyperlipidemic subjects. In HTC subjects of hyperlipidemia, the concentrations of prebeta(1)-HDL were significantly lower and HDL(2b) concentrations were significantly higher than in HTG and MHL subjects. In HTG subjects, the concentrations of HDL(3a) were significantly higher and the concentrations of HDL(2b) were lower than in HTC and MHL subjects. In total hyperlipidemic subjects, plasma triglyceride (TG) concentrations showed positive correlation with prebeta(1)-HDL, prebeta(2)-HDL, HDL(3b) and HDL(3a) and negative correlation with HDL(2a) and HDL(2b). The total cholesterol (TC) concentrations showed positive correlation with the relative apoA-I contents of prebeta(1)-HDL and HDL(3b), whereas the HDL-C concentrations showed negative correlation with the relative apoA-I contents of prebeta(1)-HDL and HDL(3a) and positive correlation with those of HDL(2a) and HDL(2b). The relative apoA-I contents of prebeta(1)-HDL, prebeta(2)-HDL, HDL(3b), and HDL(3a) were positively correlated whereas those of HDL(2a) and HDL(2b) were negatively correlated with TG/HDL-C ratio.

CONCLUSION

The particle size of HDL in hyperlipidemic subjects shifted towards smaller sizes, which, in turn, indicates that the maturation of HDL may be abnormal in hyperlipidemic subjects.

Charge-based heterogeneity of human plasma lipoproteins at hypertriglyceridemia: capillary isotachophoresis study

To reveal the metabolic links between and within pools of pro-atherogenic triglyceride(TG)-rich lipoproteins and anti-atherogenic high density lipoproteins (HDL), the changes in lipoprotein profile at hypertriglyceridemia were analyzed by capillary isotachophoresis. Plasma samples from patients with apoE3/3 phenotype were stained with a fluorescent probe NBD-C6-ceramide and lipoproteins resolved into six H-, one (V+I) and four L-components which belong to HDL, very low and intermediate density (VLDL+IDL) and low density lipoproteins (LDL), respectively. The expected correlation between the relative size of the combined fractions and lipid and apolipoprotein values was obtained confirming the validity of the approach. The new findings were obtained as follows. (1) The fast L-component correlated inversely with HDL-cholesterol (Chol), while intermediate and slow H-components correlated inversely with plasma and LDL-Chol and apoB. (2) The content of intermediate and slow H-components increased within H-pool and decreased relative TG-rich lipoproteins as hypertriglyceridemia rose due to the impairment of triglyceride hydrolysis by lipoprotein lipase within TG-rich particles. (3) A predictive value of the ratios of fast to slow H-components as an indicator of lecithin:cholesterol acyltransferase activity was demonstrated which tended to decrease at hypertriglyceridemia. (4) The L1/L2 ratio may be considered as an indicator of the accumulation of small dense LDL, which is a feature of clinically manifested atherogenic B-pattern. The competition between H(DL) and L(DL) particles for hepatic lipase and significant contribution of apoE to functional deficiency of H(DL) particles at hypertriglyceridemia are suggested.

Single session exercise stimulates formation of pre beta 1-HDL in leg muscle

Physical activity can raise the level of circulating HDL cholesterol. Pre beta 1-HDL is thought to be either the initial acceptor of cellular cholesterol or virtually the first particle in the pathway of the formation of HDL from apolipoprotein A-I and cellular lipids. We have therefore sought to identify pre beta 1-HDL in arterial and venous circulations of exercising legs in healthy individuals and in subjects with stable Type 2 diabetes mellitus. Blood samples were taken simultaneously from the femoral artery and vein before and after 25 min cycling exercise. The major findings were, first, that exercise significantly increased plasma concentration of pre beta 1-HDL (20% increase, P < 0.05) and second, that the pre beta 1-HDL concentration was significantly higher in the venous compared with the arterial blood both before and after exercise in both diabetics and controls. In the combined population, formation of pre beta 1-HDL at rest was 9.9 +/- 5.2 mg/min and exercise enhanced pre beta 1-HDL formation 6.6-fold in both groups.

Analytical performance of a sandwich enzyme immunoassay for pre beta 1-HDL in stabilized plasma

We have established an immunoassay for pre beta 1-HDL (the initial acceptor of cellular cholesterol) using a monoclonal antibody, MAb55201. Because pre beta 1-HDL is unstable during storage, fresh plasma must be used for pre beta 1-HDL measurements. In this study, we describe a method of stabilizing pre beta 1-HDL, and evaluate the analytical performance of the immunoassay for pre beta 1-HDL. Fresh plasma was stored under various conditions with or without a pretreatment consisting of a 21-fold dilution into 50% (v/v) sucrose. Pre beta 1-HDL concentration was measured by immunoassay. In nonpretreated samples, pre beta 1-HDL decreased significantly from the baseline after 6 h at room temperature. Although pre beta 1-HDL was more stable at 0 degrees C than at room temperature, it increased from 30.2 +/- 8.5 (SE) to 56.5 +/- 5.5 mg/l apolipoprotein A-I (apoA-I) (P < 0.001) in hyperlipidemics, and from 18.4 +/- 1.2 to 37.9 +/- 3.3 mg/l apoA-I (P < 0.001) in normolipidemics after 5-day storage. After 30-day storage at -80 degrees C, pre beta 1-HDL increased from 29.0 +/- 4.0 to 38.0 +/- 5.7 mg/l apoA-I (P < 0.001) in hyperlipidemics, whereas it did not change in normolipidemics. In pretreated samples, pre beta 1-HDL concentration did not change significantly under any of the above conditions. Moreover, pre beta 1-HDL concentrations determined by immunoassay correlated with those determined by native two-dimensional gel electrophoresis (n = 24, r = 0.833, P < 0.05). An immunoassay using MAb55201 with pretreated plasma is useful for clinical measurement of pre beta 1-HDL.

Delineation of the role of pre-beta 1-HDL in cholesterol efflux using isolated pre-beta 1-HDL

OBJECTIVE

The role of pre-beta1-high density lipoprotein (pre-beta1-HDL) in cholesterol efflux was investigated by separating human plasma into purified pre-beta1-HDL and pre-beta1-HDL-deficient plasma by using a monoclonal antibody specifically reacting with pre-beta1-HDL.

METHODS AND RESULTS

When compared with whole plasma, pre-beta1-HDL-deficient plasma was equally efficient in promoting cholesterol efflux from human skin fibroblasts and THP-1 human macrophage cells. When added at the same apolipoprotein A-I concentration, pre-beta1-HDL was less effective than whole plasma in promoting cholesterol efflux from fibroblasts but equally effective in promoting cholesterol efflux from THP-1 cells. However, pre-beta1-HDL-deficient plasma reconstituted with 16% pre-beta1-HDL was more active than whole plasma, demonstrating that pre-beta1-HDL does promote cholesterol efflux actively. The amount of cellular cholesterol present in reisolated pre-beta1-HDL was 1.5- to 2-fold greater after incubation of the cells with whole plasma than after incubation of the cells with pre-beta1-HDL-deficient plasma or plasma treated with the anti-pre-beta1-HDL antibody. However, the anti-pre-beta1-HDL antibody did not inhibit cholesterol efflux.

CONCLUSIONS

We conclude that whereas pre-beta1-HDL is capable of taking up cellular cholesterol, its presence in plasma is not essential for cholesterol efflux, at least in vitro. Instead, pre-beta1-HDL may be the first product of apolipoprotein A-I lipidation during the formation of HDL but may not play a major role in transferring cellular cholesterol to HDL.

Dynamics of reverse cholesterol transport: protection against atherosclerosis

This review considers the antiatherogenic function of high density lipoprotein (HDL) from the point of view of its dynamics within the sequential steps of reverse cholesterol transport (RCT). It is postulated that the efficiency of cholesterol flux through the RCT pathways is clinically more relevant than the HDL cholesterol concentration. The particular role of pre-beta(1)-HDL is reviewed drawing attention to the relationship between its concentration and the flux of cholesterol through the RCT system.

Distribution of ApoA-I-containing HDL subpopulations in patients with coronary heart disease

High density lipoproteins (HDLs) and their subspecies play a role in the development of coronary heart disease (CHD). HDL subpopulations were measured by 2-dimensional nondenaturing gel electrophoresis in 79 male control subjects and 76 male CHD patients to test the hypothesis that greater differences in apolipoprotein (apo)A-I-containing HDL subpopulations would exist between these 2 groups than for traditional lipid levels. In CHD subjects, HDL cholesterol (HDL-C) was lower (-14%, P<0.001), whereas total cholesterol and the low density lipoprotein cholesterol/HDL-C ratio were higher (9% [P:<0.05] and 21% [P:<0.01], respectively) compared with control levels. No significant differences were found for low density lipoprotein cholesterol, triglyceride, and apoA-I levels. In CHD subjects, there were significantly (P:<0.001) lower concentrations of the large lipoprotein (Lp)A-I alpha(1) (-35%), pre-alpha(1) (-50%), pre-alpha(2) (-33%), and pre-alpha(3) (-31%) subpopulations, whereas the concentrations of the small LpA-I/A-II alpha(3) particles were significantly (P:<0.001) higher (20%). Because alpha(1) was decreased more than HDL-C and plasma apoA-I concentrations in CHD subjects, the ratios of HDL-C to alpha(1) and of apoA-I to alpha(1) were significantly (P:<0.001) higher by 36% and 57%, respectively, compared with control values. Subjects with low HDL-C levels (</=35 mg/dL) have different distributions of apoA-I-containing HDL subpopulations than do subjects with normal HDL-C levels (>35 mg/dL). Therefore, we stratified participants according to HDL-C concentrations into low and normal groups. The differences in lipid levels between controls and HDL-C-matched cases substantially decreased; however, the significant differences in HDL subspecies remained. Our research findings support the concept that compared with control subjects, CHD patients not only have HDL deficiency but also have a major rearrangement in the HDL subpopulations with significantly lower alpha(1) and pre-alpha(1-3) (LpA-I) and significantly higher alpha(3) (LpA-I/A-II) particles.

Effect of weight reduction on the distribution of apolipoprotein A-I in high-density lipoprotein subfractions in obese non-insulin-dependent diabetic subjects

High-density lipoprotein (HDL) plays an important role in the process of reverse cholesterol transport, which may become suboptimal with increasing body fatness. HDL cholesterol that is reduced in obese subjects paradoxically decreases during weight reduction. To determine how weight reduction affects HDL subclasses that are involved in reverse cholesterol transport, we studied HDL from obese diabetic subjects before and after energy restriction within background diets high in either carbohydrate or monounsaturated fatty acids (MUFAs). Body weight, blood glucose, total cholesterol, and LDL cholesterol decreased after 8 and 12 weeks of weight reduction. With the very-low-fat diet, HDL cholesterol decreased significantly at 8 weeks, but recovered to initial levels after 12 weeks as body weight began to stabilize. Plasma apolipoprotein A-I (apo A-I) decreased substantially and significantly at 8 and 12 weeks with both diets, and was reflected in the reduction of apo A-I in HDL subclasses alpha1, alpha2, pre-beta1, and pre-beta2 + pre-beta3. The calculation of the percentage distribution of apo A-I among HDL species showed that only the proportion of pre-beta1-HDL decreased, whereas alpha2-HDL increased. This led to a significant increase in the alpha1 + alpha2/pre-beta ratio, ie, the ratio of the large cholesterol "storage" or "sink" HDL to the HDL "shuttle" fraction considered to be the initial acceptor of cell cholesterol. These data suggest that despite the reduction in HDL cholesterol and apo A-I, the redistribution of apo A-I in pre-beta1-HDL and alpha-HDL observed with weight reduction appears to revert to the pattern that we have previously reported in lean as opposed to overweight subjects.

Identification of a sequence of apolipoprotein A-I associated with the activation of Lecithin:Cholesterol acyltransferase

We aimed to distinguish between the effects of mutations in apoA-I on the requirements for the secondary structure and a specific amino acid sequence for lecithin:cholesterol acyltransferase (LCAT) activation. Several mutants were constructed targeting region 140-150: (i) two mutations affecting alpha-helical structure, deletion of amino acids 140-150 and substitution of Ala(143) for proline; (ii) two mutations not affecting alpha-helical structure, substitution of Val(149) for arginine and substitution of amino acids 63-73 for sequence 140-150; and (iii) a mutation in a similar region away from the target area, deletion of amino acids 63-73. All mutations affecting region 140-150 resulted in a 4-42-fold reduction in LCAT activation. Three mutations, apoA-I(Delta140-150), apoA-I(P143A), and apoA-I(140-150 --> 63-73), affected both the apparent V(max) and K(m), whereas the mutation apoA-I(R149V) affected only the V(max). The mutation apoA-I(Delta63-73) caused only a 5-fold increase in the K(m). All mutants, except apoA-I(P143A) and apoA-I(Delta63-73), were active in phospholipid binding assay. All mutants, except apoA-I(P143A), formed normal discoidal complexes with phospholipid. The mutation apoA-I(Delta63-73) caused a significant reduction in the stability of apoA-I.phospholipid complexes in denaturation experiments. Combined, our results strongly suggest that although the correct conformation and orientation of apoA-I in the complex with lipids are crucial for activation of LCAT, when these conditions are fulfilled, activation also strongly depends on the sequence that includes amino acids 140-150.

Very Small Apolipoprotein A-I-containing Particles from Human Plasma: Isolation and Quantification by High-Performance Size-Exclusion Chromatography

Background: Very small apolipoprotein (apo) A-I-containing lipoprotein (Sm LpA-I) particles with pre-β electrophoretic mobility may play key roles as “nascent” and/or “senescent” HDL; however, methods for their isolation are difficult and often semiquantitative.

Methods: We developed a preparative method for separating Sm LpA-I particles from human plasma by high-performance size-exclusion chromatography (HP-SEC), using two gel permeation columns (Superdex 200 and Superdex 75) in series and measuring apo A-I content in column fractions in 30 subjects with HDL-cholesterol (HDL-C) concentrations of 0.4–3.83 mmol/L.

Results: Three major sizes of apo A-I-containing particles were detected: an ∼15-nm diameter (∼700 kDa) species; a 7.5–12 nm (100–450 kDa) species; and a 5.8–6.3 nm species (40–60 kDa, Sm LpA-I particles), containing 0.2–3%, 80–96%, and 2–15% of plasma total apo A-I, respectively. Two subjects with severe HDL deficiency had increased relative apo A-I content in Sm LpA-I: 25% and 37%, respectively. The percentage of apo A-I in Sm LpA-I correlated positively with fasting plasma triglyceride concentrations (r = 0.581; P &lt;0.0005) and inversely with total apo A-I (r = −0.551; P &lt;0.0013) and HDL-C concentrations (r = −0.532; P &lt;0.0017), although the latter two relationships were largely attributable to extremely hypoalphalipoproteinemic subjects. The percentage of apo A-I in Sm LpA-I correlated with that in pre-β-migrating species by crossed immunoelectrophoresis (r = 0.98; P &lt;0.0001; n = 24) and with that in the d &gt;1.21 kg/L fraction by ultracentrifugation (r = 0.86; P &lt;0.001; n = 20). Sm LpA-I particles, on average, appear to contain two apo A-I and four phospholipid molecules but little or no apo A-II, triglyceride, or cholesterol.

Conclusions: We present a new HP-SEC method for size separation of native HDL particles from plasma, including Sm Lp A-I, which may play important roles in the metabolism of HDL and in its contribution(s) to protection against atherosclerosis. This method provides a basis for further studies of the structure and function of Sm Lp A-I.

Effect of apolipoprotein A-I lipidation on the formation and function of pre-beta and alpha-migrating LpA-I particles

A unique class of lipid-poor high-density lipoprotein, pre-beta1 HDL, has been identified and shown to have distinct functional characteristics associated with intravascular cholesterol transport. In this study we have characterized the structure/function properties of poorly lipidated HDL particles and the factors that mediate their conversion into multimolecular lipoprotein particles. Studies were undertaken with homogeneous recombinant HDL particles (LpA-I) containing apolipoprotein (apo) A-I and various amounts of palmitoyloleoylphosphatidylcholine (PC) and cholesterol. Complexation of apoA-I with small amounts of PC and cholesterol results in the formation of discrete lipoprotein structures that have a hydrated diameter of about 6 nm but contain only one molecule of apoA-I (Lp1A-I). While the molecular charge and alpha-helix content of apoA-I are unaffected by lipidation, the thermodynamic stability of the protein is reduced significantly (from 2.4 to 0.9 kcal/mol of apoA-I). Evaluation of apoA-I conformation by competitive radioimmunoassay with monoclonal antibodies shows that addition of small amounts of PC and cholesterol to apoA-I significantly increases the immunoreactivity of a number of domains over the entire molecule. Increasing the ratio of PC:apoA-I to 10:1 in the Lp1A-I complex is associated with increases in the alpha-helix content and stability of apoA-I. However, incorporation of 10-15 mol of PC destabilizes the Lp1A-I complex and promotes the formation of more thermodynamically stable (1.8 kcal/mol of apoA-I) bimolecular structures (Lp2A-I) that are approximately 8 nm in diameter. The formation of an Lp2A-I particle is associated with an increased immunoreactivity of most of the epitopes studied, with the exception of one central domain (residues 98-121), which becomes significantly less exposed. This structural change parallels a significant increase in the net negative charge on the complex. Characterization of the ability of these lipoproteins to act as substrates for lecithin:cholesterol acyltransferase (LCAT) shows that unstable Lp1A-I complexes stimulate a higher rate of cholesterol esterification by LCAT than the small but more stable Lp2A-I particles (Vmax values are 5.8 and 0.3 nmol of free cholesterol esterified/h, respectively). The ability of LCAT to interact with lipid-poor apoA-I suggests that LCAT does not need to bind to the lipid interface on an HDL particle but that LCAT may directly interact with apoA-I. The data suggests that lipid-poor HDL particles may be metabolically reactive particles because they are thermodynamically unstable.