Effects of weight loss,induced by gastric bypass surgery,on HDL remodeling in obese women

Plasma lipoproteins and glucose homeostasis were evaluated after marked weight loss before and over 12 months following Roux-en-Y gastric-bypass (RYGBP) surgery in 19 morbidly obese women. Standard lipids, remnant-lipoprotein cholesterol (RLP-C); HDL-triglyceride (TG); apolipoproteins (apo) A-I, A-II, E, and A-I-containing HDL subpopulations; lecithin-cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) mass and activity; plasma glucose and insulin levels were measured before and at 1, 3, 6, and 12 months after GBP surgery. Baseline concentrations of TG, RLP-C, glucose, and insulin were significantly higher in obese than in normal-weight, age-matched women, whereas HDL cholesterol (HDL-C), apoA-I, apoA-II, α-1 and α-2 levels were significantly lower. Over 1 year, significant decreases of body mass index, glucose, insulin, TG, RLP-C, HDL-TG, and preβ-1 levels were observed with significant increases of HDL-C and α-1 levels (all P < 0.05). Changes of fat mass were correlated with those of LDL cholesterol (P = 0.018) and LCAT mass (P = 0.011), but not with CETP mass (P = 0.265). Changes of fasting plasma glucose concentrations were inversely correlated with those of CETP mass (P = 0.005) and α-1 level (P = 0.004). Changes of fasting plasma insulin concentrations were positively correlated with those of LCAT mass (P = 0.043) and inversely with changes of α-1 (P = 0.03) and α-2 (P = 0.05) concentrations. These results demonstrate beneficial changes in HDL remodeling following substantial weight loss induced by RYGBP surgery and that these changes are associated with improvement of glucose homeostasis in these patients.     

Lower HDL-C and apolipoprotein A-I are related to higher glomerular filtration rate in subjects without kidney disease

Animal experiments show that the kidney contributes to apolipoprotein (apo)A-I catabolism. We tested relationships of HDL cholesterol (HDL-C) and apo-I with kidney function in subjects without severe chronic kidney disease. Included was a random sample of the general population (part of the PREVEND cohort). Kidney function [estimated glomerular filtration rate (e-GFR) by two well-established equations and creatinine clearance], HDL-C, triglycerides, apoA-I and insulin resistance (HOMA_ir) were measured in 2,484 fasting subjects (e-GFR≥45 ml/min/1.73m²) without macroalbuminuria, cardiovascular disease, diabetes, or the use of anti-hypertensives and/or lipid-lowering agents. HDL-C (r = −0.056 to −0.102, P < 0.01 to < 0.001) and apo A-I (r = −0.096 to −0.126, P < 0.001) were correlated inversely with both GFR estimates and creatinine clearance in univariate analyses. Multiple linear regression analyses also demonstrated inverse relationships of HDL-C and apoA-I with all measures of kidney function even after adjustment for age, sex, waist circumference, HOMA_ir, triglycerides, and urinary albumin excretion (P = 0.053 to 0.004). In conclusion, HDL-C and apoA-I are inversely related to e-GFR and creatinine clearance in subjects without severely compromised kidney function, which fits the concept that the kidney contributes to apoA-I regulation in humans. High glomerular filtration rate may be an independent determinant of a pro-atherogenic lipoprotein profile.     

Importance of macrophage cholesterol content on the flux of cholesterol mass

Net flux of cholesterol represents the difference between efflux and influx and can result in net cell-cholesterol accumulation, net cell-cholesterol depletion, or no change in cellular cholesterol content. We measured radiolabeled cell-cholesterol efflux and cell-cholesterol mass using cholesterol-normal and -enriched J774 and elicited mouse peritoneal macrophage cells. Net cell-cholesterol effluxes were observed when cholesterol-enriched J774 cells were incubated with 3.5% apolipoprotein (apo) B depleted human serum, HDL₃, and apo A-I. Net cell-cholesterol influxes were observed when cholesterol-normal J774 cells were incubated with the same acceptors except apo A-I. When incubated with 2.5% individual sera, cholesterol mass efflux in free cholesterol (FC)-enriched J774 cells correlated with the HDL-cholesterol (HDL-C) concentrations (r² = 0.4; P=0.003), whereas cholesterol mass influx in cholesterol-normal J774 cells correlated with the LDL cholesterol (LDL-C) concentrations (r² = 0.6; P<0.0001) of the individual sera. A positive correlation was observed between measurements of [³H]cholesterol efflux and reductions in cholesterol mass (r² = 0.4; P=0.001) in FC-enriched J774 cells. In conclusion, isotopic efflux measurements from cholesterol-normal or cholesterol-enriched cells provide an accurate measurement of relative ability of an acceptor to remove labeled cholesterol under a specific set of experimental conditions, i.e., efflux potential. Moreover, isotopic efflux measurements can reflect changes in cellular cholesterol mass if the donor cells are enriched with cholesterol.     

Human plasma phospholipid transfer protein specific activity is correlated with HDL size: Implications for lipoprotein physiology

To gain further insights into the relationship between plasma phospholipid transfer protein (PLTP) and lipoprotein particles, PLTP mass and phospholipid transfer activity were measured, and their associations with the level and size of lipoprotein particles examined in 39 healthy adult subjects. No bivariate correlation was observed between PLTP activity and mass. PLTP activity was positively associated with cholesterol, triglyceride, apo B and VLDL particle level (r_s = 0.40–0.56, p ≤ 0.01) while PLTP mass was positively associated with HDL-C, large HDL particles, and mean LDL and HDL particle sizes (r_s = 0.44–0.52, p < 0.01). Importantly, plasma PLTP specific activity (SA) was significantly associated with specific lipoprotein classes, positively with VLDL, IDL, and small LDL particles (r_s = 0.42–0.62, p ≤ 0.01) and inversely with large LDL, large HDL, and mean LDL and HDL particle size (r_s = − 0.42 to − 0.70, p ≤ 0.01). After controlling for triglyceride levels, the correlation between PLTP mass or SA and HDL size remained significant. In linear models, HDL size explained 45% of the variability of plasma PLTP SA while triglyceride explained 34% of the PLTP activity. Thus, in healthy adults a significant relationship exists between HDL size and plasma PLTP SA (r_s = − 0.70), implying that HDL particle size may modulate PLTP SA in the vascular compartment.     

Defective functionality of HDL particles in familial apoA-I deficiency: relevance of alterations in HDL lipidome and proteome

To evaluate functional and compositional properties of HDL in subjects from a kindred of genetic apoA-I deficiency, two homozygotes and six heterozygotes, with a nonsense mutation at APOA1 codon -2, Q[-2]X, were recruited together with age- and sex-matched healthy controls (n = 11). Homozygotes displayed undetectable plasma levels of apoA-I and reduced levels of HDL-cholesterol (HDL-C) and apoC-III (5.4% and 42.6% of controls, respectively). Heterozygotes displayed low HDL-C (21 ± 9 mg/dl), low apoA-I (79 ± 24 mg/dl), normal LDL-cholesterol (132 ± 25 mg/dl), and elevated TG (130 ± 45 mg/dl) levels. Cholesterol efflux capacity of ultracentrifugally isolated HDL subpopulations was reduced (up to −25%, P < 0.01, on a glycerophospholipid [GP] basis) in heterozygotes versus controls. Small, dense HDL3 and total HDL from heterozygotes exhibited diminished antioxidative activity (up to −48%, P < 0.001 on a total mass basis) versus controls. HDL subpopulations from both homozygotes and heterozygotes displayed altered chemical composition, with depletion in apoA-I, GP, and cholesteryl ester; enrichment in apoA-II, free cholesterol, and TG; and altered phosphosphingolipidome. The defective atheroprotective activities of HDL were correlated with altered lipid and apo composition. These data reveal that atheroprotective activities of HDL particles are impaired in homozygous and heterozygous apoA-I deficiency and are intimately related to marked alterations in protein and lipid composition.     

Dalcetrapib and anacetrapib increase apolipoprotein E-containing HDL in rabbits and humans

The large HDL particles generated by administration of cholesteryl ester transfer protein inhibitors (CETPi) remain poorly characterized, despite their potential importance in the routing of cholesterol to the liver for excretion, which is the last step of the reverse cholesterol transport. Thus, the effects of the CETPi dalcetrapib and anacetrapib on HDL particle composition were studied in rabbits and humans. The association of rabbit HDL to the LDL receptor (LDLr) in vitro was also evaluated. New Zealand White rabbits receiving atorvastatin were treated with dalcetrapib or anacetrapib. A subset of patients from the dal-PLAQUE-2 study treated with dalcetrapib or placebo were also studied. In rabbits, dalcetrapib and anacetrapib increased HDL-C by more than 58% (P < 0.01) and in turn raised large apo E-containing HDL by 66% (P < 0.001) and 59% (P < 0.01), respectively. Additionally, HDL from CETPi-treated rabbits competed with human LDL for binding to the LDLr on HepG2 cells more than control HDL (P < 0.01). In humans, dalcetrapib increased concentrations of large HDL particles (+69%, P < 0.001) and apo B-depleted plasma apo E (+24%, P < 0.001), leading to the formation of apo E-containing HDL (+47%, P < 0.001) devoid of apo A-I. Overall, in rabbits and humans, CETPi increased large apo E-containing HDL particle concentration, which can interact with hepatic LDLr. The catabolism of these particles may depend on an adequate level of LDLr to contribute to reverse cholesterol transport.     

Stimulation of lecithin:cholesterol acyltransferase activity by apolipoprotein A-II in the presence of apolipoprotein A-I

Various combinations of incorporation and addition of apolipoprotein A-I (apo A-I) and apolipoprotein A-II (apo A-II) individually or together to a defined lecithin-cholesterol (250/12.5 molar ratio) liposome prepared by the cholate dialysis procedure were used to study the effect of apo A-II on lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) activity of both purified enzyme preparations and plasma. When apo A-I (0.1-3.0 nmol/assay) alone was incorporated or added to the liposome, apo A-I effectively activated the enzyme. By contrast, when apo A-II (0.1-3.0 nmol/assay) alone was incorporated into or added to the liposome, apo A-II exhibited minimal activation of LCAT activity, approximately 1% of the activity obtained by an equal amount of apo A-I. Addition of apo A-II (0.1-3.0 nmol/assay) together with apo A-I (0.8 nmol/assay) to the liposome reduced the LCAT activity to approximately 30% of the level obtained with addition of apo A-I alone. On the other hand, addition of apo A-II (0.1-3.0 nmol/assay) or addition of lecithin-cholesterol liposome containing apo A-II (0.1-3.0 nmol/assay) to lecithin-cholesterol liposome containing apo A-I (0.8 nmol/assay) did not significantly alter apo A-I activation of LCAT activity. However, when the same amounts (0.1-3.0 nmol/assay) of apo A-II were incorporated together with apo A-I (0.8 nmol/assay) into the liposome, apo A-II significantly stimulated LCAT activity as compared to activity obtained with incorporation of apo A-I alone. The maximal stimulation was obtained with 0.4 nmol apo A-II/assay for both purified and plasma enzyme. At this apo A-II concentration, approximately 4-fold and 1.8-fold stimulation was observed for purified enzyme and plasma enzyme, respectively. These results indicated that apo A-II must be incorporated together with apo A-I into lecithin-cholesterol liposomes to exert its stimulatory effect on LCAT activity and that apo A-II in high-density lipoprotein may play an important role in the regulation of LCAT activity.     

Human apo A-I in transgenic mice is more efficient in activating lecithin: cholesterol acyltransferase than mouse apo A-I

This study shows that, in control and transgenic mice, there is a parallel increase in LCAT activity and plasma apo A-I concentrations during postnatal development. We also demonstrate that human apo A-I is a much more efficient activator (1.6-fold) of mouse LCAT activity than mouse apo A-I. We propose that the differences in amino acid sequence between human and mouse apo A-I may account for the higher LCAT activity with human apo A-I.     

Formation of spherical, reconstituted high density lipoproteins containing both apolipoproteins A-I and A-II is mediated by lecithin:cholesterol acyltransferase

Previous studies have provided detailed information on the formation of spherical high density lipoproteins (HDL) containing apolipoprotein (apo) A-I but no apoA-II (A-I HDL) by an lecithin:cholesterol acyltransferase (LCAT)-mediated process. In this study we have investigated the formation of spherical HDL containing both apoA-I and apoA-II (A-I/A-II HDL). Incubations were carried out containing discoidal A-I reconstituted HDL (rHDL), discoidal A-II rHDL, and low density lipoproteins in the absence or presence of LCAT. After the incubation, the rHDL were reisolated and subjected to immunoaffinity chromatography to determine whether A-I/A-II rHDL were formed. In the absence of LCAT, the majority of the rHDL remained as either A-I rHDL or A-II rHDL, with only a small amount of A-I/A-II rHDL present. By contrast, when LCAT was present, a substantial proportion of the reisolated rHDL were A-I/A-II rHDL. The identity of the particles was confirmed using apoA-I rocket electrophoresis. The formation of the A-I/A-II rHDL was influenced by the relative concentrations of the precursor discoidal A-I and A-II rHDL. The A-I/A-II rHDL included several populations of HDL-sized particles; the predominant population having a Stokes' diameter of 9.9 nm. The particles were spherical in shape and had an electrophoretic mobility slightly slower than that of the alpha-migrating HDL in human plasma. The apoA-I:apoA-II molar ratio of the A-I/A-II rHDL was 0.7:1. Their major lipid constituents were phospholipids, unesterified cholesterol, and cholesteryl esters. The results presented are consistent with LCAT promoting fusion of the A-I rHDL and A-II rHDL to form spherical A-I/A-II rHDL. We suggest that this process may be an important source of A-I/A-II HDL in human plasma.     

Influence of inflammatory response,infection, and pulmonary function in cystic fibrosis

Aims

Recurrent infections and activation of the inflammatory response affect the prognosis of cystic fibrosis (CF). We investigated the relationship between inflammatory response, infection, and pulmonary function in CF.

Main methods

A clinical-cross-sectional study was conducted with 86 subjects: control group (CG, n = 31, the same age and sex of the CF group), and CF group (CFG, n = 55, age: 1–16 years), further distributed into CFG negative or positive bacteriology (CFGB⁻/CFGB⁺), and CFG negative or positive Pseudomonas aeruginosa (CFGPa⁻/CFGPa⁺). Using the Wald test, multiple linear regression (95% confidence interval) was performed between CG and CFG, and between CG and each of the CF subgroups (CFGB⁻/CFGB⁺ and CFGPa⁻/CFGPa⁺). The inflammatory markers evaluated were myeloperoxidase (MPO), adenosine deaminase (ADA) activities, interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), C-reactive protein (CRP), nitric oxide metabolites (NOx) levels, and total and differential leukocyte counts.

Key findings

After adjusting for sex and age, CFG compared to CG revealed an increase of MPO, IL-1β (P < 0.001 in all subgroups), and CRP: CFG (P = 0.002), CFGB⁻ (P = 0.007), CFGB⁺ (P = 0.009), CFGPa⁻ (P = 0.004) and CFGPa⁺ (P = 0.020). NOx (P = 0.001, P < 0.001), leukocytes (P = 0.002, P = 0.001), and neutrophils (P = 0.003, P < 0.001) were increased in CFGB⁺ and CFGPa⁺, respectively. A negative correlation between FEV₁ and leukocytes (P = 0.008) and FEV₁ and neutrophils (P = 0.031) resulted in CFG.

Significance

The inflammatory response characterized by the increase of MPO, IL-1β, and CRP is determinant for CF. Also leukocytosis due to neutrophilia determines the pulmonary function deficiency in this disease.     

LCAT deficiency in mice is associated with a diminished adrenal glucocorticoid function

In vitro studies have suggested that HDL and apoB-containing lipoproteins can provide cholesterol for synthesis of glucocorticoids. Here we assessed adrenal glucocorticoid function in LCAT knockout (KO) mice to determine the specific contribution of HDL-cholesteryl esters to adrenal glucocorticoid output in vivo. LCAT KO mice exhibit an 8-fold higher plasma free cholesterol-to-cholesteryl ester ratio (P < 0.001) and complete HDL-cholesteryl ester deficiency. ApoB-containing lipoprotein and associated triglyceride levels are increased in LCAT KO mice as compared with C57BL/6 control mice (44%; P < 0.05). Glucocorticoid-producing adrenocortical cells within the zona fasciculata in LCAT KO mice are devoid of neutral lipids. However, adrenal weights and basal corticosterone levels are not significantly changed in LCAT KO mice. In contrast, adrenals of LCAT KO mice show compensatory up-regulation of genes involved in cholesterol synthesis (HMG-CoA reductase; 516%; P < 0.001) and acquisition (LDL receptor; 385%; P < 0.001) and a marked 40–50% lower glucocorticoid response to adrenocorticotropic hormone exposure, endotoxemia, or fasting (P < 0.001 for all). In conclusion, our studies show that HDL-cholesteryl ester deficiency in LCAT KO mice is associated with a 40–50% lower adrenal glucocorticoid output. These findings further highlight the important novel role for HDL as cholesterol donor for the synthesis of glucocorticoids by the adrenals.     

Increased risk of coronary artery disease in Caucasians with extremely low HDL cholesterol due to mutations in ABCA1, APOA1, and LCAT

Mutations in ABCA1, APOA1, and LCAT reduce HDL cholesterol (HDLc) in humans. However, the prevalence of these mutations and their relative effects on HDLc reduction and risk of coronary artery disease (CAD) are less clear. Here we searched for ABCA1, APOA1, and LCAT mutations in 178 unrelated probands with HDLc < 10th percentile but no other major lipid abnormalities, including 89 with ≥ 1 first-degree relative with low HDLc (familial probands) and 89 where familial status of low HDLc is uncertain (unknown probands). Mutations were most frequent in LCAT (15.7%), followed by ABCA1 (9.0%) and APOA1 (4.5%), and were found in 42.7% of familial but only 14.6% of unknown probands (p = 2.44 ∗ 10^− 5). Interestingly, only 16 of 24 (66.7%) mutations assessed in families conferred an average HDLc < 10th percentile. Furthermore, only mutation carriers with HDLc < 5th percentile had elevated risk of CAD (odds ratio (OR) = 2.26 for 34 ABCA1 mutation carriers vs. 149 total first-degree relative controls, p = 0.05; OR = 2.50 for 26 APOA1 mutation carriers, p = 0.04; OR = 3.44 for 38 LCAT mutation carriers, p = 1.1 ∗ 10^− 3). These observations show that mutations in ABCA1, APOA1, and LCAT are sufficient to explain > 40% of familial hypoalphalipoproteinemia in this cohort. Moreover, individuals with mutations and large reductions in HDLc have increased risk of CAD. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).     

Accumulation of cholestatic lipoproteins in ANIT-treated human apolipoprotein A-I transgenic rats is diminished through dose-dependent apolipoprotein A-I activation of LCAT

Administration of alpha-naphthylisothiocyanate (ANIT) to rats induces changes to plasma lipids consistent with cholestasis. We have previously shown (J. Lipid Res. 37 (1996) 1086) that animals treated with ANIT accumulate large amounts of free cholesterol (FC) and phospholipid (PL)-rich cholestatic lipoproteins in the LDL density range by 48 h. This lipid was cleared by 120 h through apparent movement into HDL with concomitant cholesteryl ester (CE) production. It was hypothesised that the clearance was mediated through the movement of the PL and FC into apolipoprotein A-I (apo A-I) containing lipoproteins followed by LCAT esterification to form CE. To test this hypothesis, rats overexpressing various amounts of human apo A-I (TgR[HuAI] rats) were treated with ANIT (100 mg/kg) and the effect of plasma apo A-I concentration on plasma lipids and lipoprotein distribution was examined. In untreated TgR[HuAI] rats, human apo A-I levels were strongly correlated to plasma PL (r(2)=0. 94), FC (r(2)=0.93) and CE (r(2)=0.90), whereas in ANIT-treated TgR[HuAI] rats, human apo A-I levels were most strongly correlated to CE levels (r(2)=0.80) and an increased CE/FC ratio (r(2)=0.62) and the movement of cholestatic lipid in the LDL to HDL. Since LCAT activity was not affected by ANIT treatment, these results demonstrate that the ability of LCAT to esterify the plasma FC present in cholestatic liver disease is limited by in vivo apo A-I activation of the cholestatic lipid and not by the catalytic capacity of LCAT.     

The ability of plasma to stimulate fibroblast cholesterol efflux is associated with the -629C-->A cholesteryl ester transfer protein promoter polymorphism: role of lecithin: cholesterol acyltransferase activity

A recent population-based study showed that cholesteryl ester transfer protein (CETP) gene variations, which relate to lower plasma CETP, may predict increased cardiovascular risk, in spite of higher HDL cholesterol. Among other functions, CETP activity contributes to cellular cholesterol efflux, an early step in the anti-atherogenic reverse cholesterol transport (RCT) process. We hypothesized that cellular cholesterol efflux stimulating capacity of plasma could be associated with CETP gene variation. In this study, we tested the extent to which the ability of plasma to promote cholesterol efflux from cultured human fibroblasts is associated with CETP gene variation. In 223 men, the -629C-->A CETP promoter polymorphism, plasma lipids, CETP mass, cholesteryl ester transfer (CET), lecithin:cholesterol acyltransferase (LCAT) activity and the ability of plasma to promote cholesterol efflux from human skin fibroblasts, obtained from a single normolipidemic donor, were determined. In -629CC homozygotes (n=52), cholesterol efflux, plasma CETP mass, CET and LCAT activity were higher, whereas HDL cholesterol was lower compared to -629 AA homozygotes (n=62) and -629CA+AA carriers (n=171) (P<0.05 to P<0.001). Univariate correlation analysis showed that cellular cholesterol efflux was related to CETP genotype (P=0.04), plasma CET (P<0.05), LCAT activity (P<0.001) and apo A-I (P<0.05). Multiple linear regression analysis confirmed the independent association of cellular cholesterol efflux to plasma with CETP genotype. In conclusion, an association of cellular cholesterol efflux with the -629C-->A CETP polymorphism, possibly also involving LCAT activity, could provide a mechanism explaining why CETP gene variation, which relates to lower plasma CETP, does not confer diminished cardiovascular risk.     

An apoA-I mimetic peptide increases LCAT activity in mice through increasing HDL concentration

Lecithin cholesterol acyltransferase (LCAT) plays a key role in the reverse cholesterol transport (RCT) process by converting cholesterol to cholesteryl ester to form mature HDL particles, which in turn deliver cholesterol back to the liver for excretion and catabolism. HDL levels in human plasma are negatively correlated with cardiovascular risk and HDL functions are believed to be more important in atheroprotection. This study investigates whether and how D-4F, an apolipoprotein A-I (apoA-I) mimetic peptide, influences LCAT activity in the completion of the RCT process. We demonstrated that the apparent rate constant value of the LCAT enzyme reaction gives a measure of LCAT activity and determined the effects of free metals and a reducing agent on LCAT activity, showing an inhibition hierarchy of Zn²⁺>Mg²⁺>Ca²⁺ and no inhibition with β-mercaptoethanol up to 10 mM. We reconstituted nano-disc particles using apoA-I or D-4F with phospholipids. These particles elicited good activity in vitro in the stimulation of cholesterol efflux from macrophages through the ATP-binding cassette transporter A1 (ABCA1). With these particles we studied the LCAT activity and demonstrated that D-4F did not activate LCAT in vitro. Furthermore, we have done in vivo experiments with apoE-null mice and demonstrated that D-4F (20 mg/kg body weight, once daily subcutaneously) increased LCAT activity and HDL level as well as apoA-I concentration at 72 hours post initial dosing. Finally, we have established a correlation between HDL concentration and LCAT activity in the D-4F treated mice.     

Plasma levels of lecithin:cholesterol acyltransferase and risk of future coronary artery disease in apparently healthy men and women: a prospective case-control analysis nested in the EPIC-Norfolk population study

LCAT plays a key role in the maturation of HDL, as evidenced by low HDL-cholesterol levels in carriers of deleterious mutations in LCAT. However, the role of LCAT in atherosclerosis is unclear. We set out to study this in a prospective study. Plasma LCAT levels, which strongly correlate with LCAT activity, were measured in baseline nonfasting samples of 933 apparently healthy men and women who developed coronary artery disease (CAD) and 1,852 matched controls who remained free of CAD during 6 year follow-up. LCAT levels did not differ between cases and controls but were higher in women than men. Stratification into LCAT quartiles revealed a positive association with plasma LDL-cholesterol and triglyceride levels in the unexpected absence of an association with HDL-cholesterol. In mixed-gender analyses, the odds ratio (OR) for future CAD in the highest LCAT quartile versus the lowest was 1.00 [confidence interval (CI): 0.76–1.29, P for linearity = 0.902], although opposite trends were observed in men and women. In fact, high LCAT levels were associated with an increased CAD risk in women (unadjusted OR 1.45, CI: 0.94–2.22, P for linearity = 0.036). In contrast to our studies in carriers of LCAT mutations, the current data show that low LCAT plasma levels are not associated with increased atherosclerosis in the general population.     

Inclusion of calcium during isolation of high-density lipoprotein from plasma maintains antioxidant function

We investigated how inclusion of calcium during isolation of high-density lipoprotein (HDL) affected its antioxidant function. Following isolation, HDL was dialyzed against 0.154 M NaCl without or with added calcium (1 mM). HDL’s paraoxonase 1 activity was unaffected by calcium treatment (87 ± 11% of normal vs. 89 ± 16% of normal, P = 0.826). In contrast, whereas HDL dialyzed with calcium inhibited oxidation of low-density lipoprotein (LDL) by 87 ± 10%, HDL dialyzed without calcium inhibited oxidation by only 58 ± 19% (P = 0.004). Thus, inclusion of calcium during isolation is important for maintaining HDL’s antioxidant function.     

Apolipoprotein M promotes mobilization of cellular cholesterol in vivo

Objective

The HDL associated apolipoprotein M (apoM) protects against experimental atherosclerosis but the mechanism is unknown. ApoM increases preβ-HDL formation. We explored whether plasma apoM affects mobilization of cholesterol from peripheral cells in mice.

Methods and results

ApoM-enriched HDL from apoM-transgenic mice increased the in vitro efflux of ³H-cholesterol from macrophages by 24 ± 3% (p < 0.05) as compared with HDL from wild type (WT) mice, thus confirming previous findings. However, apoM-free HDL was not poorer than that of WT HDL to mobilize ³H-cholesterol. ³H-cholesterol-labeled foam cells were implanted in the peritoneal cavity of apoM^−/−, WT and apoM-transgenic mice to assess the mobilization of cholesterol from foam cells in vivo and subsequent excretion into feces. The results showed a statistically non-significant trend towards increased mobilization of cellular cholesterol to plasma with increasing plasma apoM. However, the apoM-genotype did not affect the excretion of ³H-cholesterol in feces. Nevertheless, when apoM^−/−, apoM-transgenic and WT mice received a constant intravenous infusion of ¹³C₂-cholesterol/intralipid for 5 h, the rate of enrichment of blood free cholesterol with free ¹³C₂-cholesterol was significantly lower (consistent with an increase in flux of unlabeled free cholesterol into the plasma) in the apoM-transgenic (3.0 ± 0.9‰/h) as compared to WT (5.7 ± 0.9‰/h, p < 0.05) and apoM^−/− (6.5 ± 0.6‰/h, p < 0.01) mice.

Conclusion

The present data indicate that the plasma apoM levels modulate the ability of plasma to mobilize cellular cholesterol, whereas apoM has no major effect on the excretion of cholesterol into feces.