Binding Folate Receptor Alpha Autoantibody Is a Biomarker for Leucovorin Treatment Response in Autism Spectrum Disorder

Autism spectrum disorder (ASD) affects up to 1 in 36 children in the United States. It is a heterogeneous neurodevelopmental disorder with life-long consequences. Patients with ASD and folate pathway abnormalities have demonstrated improved symptoms after treatment with leucovorin (folinic acid), a reduced form of folate. However, biomarkers for treatment response have not been well investigated and clinical trials are lacking. In this retrospective analysis, a cohort of prospectively collected data from 110 consecutive ASD clinic patients [mean (SD) age: 10.5 (6.2) years; 74% male] was examined. These patients all underwent testing for folate receptor alpha autoantibodies (FRAAs) and soluble folate binding proteins (sFBPs) biomarkers and were treated with leucovorin, if appropriate. Analyses examined whether these biomarkers could predict response to leucovorin treatment as well as the severity of ASD characteristics at baseline. The social responsiveness scale (SRS), a measure of core ASD symptoms, and the aberrant behavior checklist (ABC), a measure of disruptive behavior, were collected at each clinic visit. Those positive for sFBPs had more severe ASD symptoms, and higher binding FRAA titers were associated with greater ABC irritability. Treatment with leucovorin improved most SRS subscales with higher binding FRAA titers associated with greater response. Leucovorin treatment also improved ABC irritability. These results confirm and expand on previous studies, underscore the need for biomarkers to guide treatment of folate pathways in ASD, and suggest that leucovorin may be effective for children with ASD.

The Soluble Folate Receptor in Autism Spectrum Disorder: Relation to Autism Severity and Leucovorin Treatment

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder with life-long consequences that affects up to 1 in 44 children. Treatment with leucovorin (folinic acid), a reduced form of folate, has been shown to improve symptoms in those with ASD and folate pathway abnormalities in controlled clinical trials. Although soluble folate binding proteins (sFBPs) have been observed in the serum of some patients with ASD, the significance of this finding has not been studied. Here, we present a cohort of ASD patients with sFBPs. These patients had severe ASD and were medically complex. Using baseline controlled open-label methodology and standardized assessments, these patients were found to improve in both core and associated ASD symptoms with leucovorin treatment. No adverse effects were related to leucovorin treatment. This is the first report of the sFBPs in ASD. This study complements ongoing controlled clinical trials and suggests that leucovorin may be effective for children with ASD who are positive for sFBPs. Further, sFBPs might be important biomarkers for treatment response to leucovorin in children with ASD. This study paves the way for further controlled studies for patients with sFBPs.

Choline Supplementation Does Not Promote Atherosclerosis in CETP-Expressing Male Apolipoprotein E Knockout Mice

Dietary trimethylamines, such as choline, metabolized by intestinal microbiota to trimethylamine are absorbed by the gut and oxidized to trimethylamine N-oxide (TMAO). The objective of this study was to determine the effect of choline supplementation on atherosclerosis progression in Apoe^−/− mice expressing human cholesterol ester transfer protein (hCETP) using the same diets as in previously reported studies. Mice expressing hCETP, after transfection with AAV2/8-hCETP, were fed an 18% protein diet with either 0.09% (standard chow), 0.5% or 1% choline for 16 weeks. Control mice not transfected with hCETP were fed 1% choline. Dietary choline supplementation increased plasma TMAO levels at 8 and 16 weeks. When atherosclerotic lesions were measured in the thoracic aorta and aortic root, there were no differences between any of the treatment groups in the amount of plaque development at either site. Throughout the study, no significant changes in plasma lipids or major classes of lipoproteins were observed in hCETP-expressing mice. Plasma-oxidized low density lipoprotein, myeloperoxidase and high density lipoprotein inflammatory index were measured at 16 weeks, with no significant changes in any of these inflammatory markers between the four treatment groups. Despite increasing plasma TMAO levels, dietary choline supplementation in Apoe^−/− mice expressing hCETP did not promote atherosclerosis.

Anti-Inflammatory HDL Function, Incident Cardiovascular Events, and Mortality: A Secondary Analysis of the JUPITER Randomized Clinical Trial

Background

High‐density lipoprotein (HDL) cholesterol has inverse association with cardiovascular disease. HDL possesses anti‐inflammatory properties in vitro, but it is unknown whether this may be protective in individuals with inflammation.

Methods and Results

The functional capacity of HDL to inhibit oxidation of oxidized low‐density lipoprotein (ie, the HDL inflammatory index; HII) was measured at baseline and 12 months after random allocation to rosuvastatin or placebo in a nested case‐control study of the JUPITER (Justification for the Use of Statins in Prevention: An Intervention Evaluating Rosuvastatin) trial. There were 517 incident cases of cardiovascular disease and all‐cause mortality compared to 517 age‐ and sex‐matched controls. Multivariable conditional logistic regression was used to examine associations of HII with events. Median baseline HII was 0.54 (interquartile range, 0.50–0.59). Twelve months of rosuvastatin decreased HII by a mean of 5.3% (95% CI, −8.9% to −1.7%; P=0.005) versus 1.3% (95% CI, −6.5% to 4.0%; P=0.63) with placebo (P=0.22 for between‐group difference). HII had a nonlinear relationship with incident events. Compared with the reference group (HII 0.5–1.0) with the lowest event rates, participants with baseline HII ≤0.5 had significantly increased risk of cardiovascular disease/mortality (adjusted hazard ratio, 1.53; 95% CI, 1.06–2.21; P=0.02). Furthermore, there was significant (P=0.002) interaction for HDL particle number with HII, such that having more HDL particles was associated with decreased risk only when HDL was anti‐inflammatory.

Conclusions

In JUPITER participants recruited on the basis of chronic inflammation, HII was associated with incident cardiovascular disease/mortality, with an optimal anti‐inflammatory HII range between 0.5 and 1.0. This nonlinear relationship of anti‐inflammatory HDL function with risk may account in part for the HDL paradox.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT00239681.

Changes in High-Density Lipoprotein Cholesterol Efflux Capacity After Bariatric Surgery Are Procedure Dependent

OBJECTIVE

High-density lipoprotein cholesterol efflux capacity (CEC) is inversely associated with incident cardiovascular events, independent of high-density lipoprotein cholesterol. Obesity is often characterized by impaired high-density lipoprotein function. However, the effects of different bariatric surgical techniques on CEC have not been compared. This study sought to determine the effects of Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) on CEC.

APPROACH AND RESULTS

We prospectively studied severely obese, nondiabetic, premenopausal Hispanic women not using lipid medications undergoing RYGB (n=31) or SG (n=36). Subjects were examined before and at 6 and 12 months after surgery. There were no differences in baseline characteristics between surgical groups. Preoperative CEC correlated most strongly with Apo A1 (apolipoprotein A1) concentration but did not correlate with body mass index, waist:hip, high-sensitivity C-reactive protein, or measures of insulin resistance. After 6 months, SG produced superior response in high-density lipoprotein cholesterol and Apo A1 quantity, as well as global and non-ABCA1 (ATP-binding cassette transporter A1)-mediated CEC (P=0.048, P=0.018, respectively) versus RYGB. In multivariable regression models, only procedure type was predictive of changes in CEC (P=0.05). At 12 months after SG, CEC was equivalent to that of normal body mass index control subjects, whereas it remained impaired after RYGB.

CONCLUSIONS

SG and RYGB produce similar weight loss, but contrasting effects on CEC. These findings may be relevant in discussions about the type of procedure that is most appropriate for a particular obese patient. Further study of the mechanisms underlying these changes may lead to improved understanding of the factors governing CEC and potential therapeutic interventions to maximally reduce cardiovascular disease risk in both obese and nonobese patients.

Cholesterol Efflux Capacity, High-Density Lipoprotein Particle Number, and Incident Cardiovascular Events: An Analysis From the JUPITER Trial (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin)

BACKGROUND

Recent failures of drugs that raised high-density lipoprotein (HDL) cholesterol levels to reduce cardiovascular events in clinical trials have led to increased interest in alternative indices of HDL quality, such as cholesterol efflux capacity, and HDL quantity, such as HDL particle number. However, no studies have directly compared these metrics in a contemporary population that includes potent statin therapy and low low-density lipoprotein cholesterol.

METHODS

HDL cholesterol levels, apolipoprotein A-I, cholesterol efflux capacity, and HDL particle number were assessed at baseline and 12 months in a nested case-control study of the JUPITER trial (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin), a randomized primary prevention trial that compared rosuvastatin treatment to placebo in individuals with normal low-density lipoprotein cholesterol but increased C-reactive protein levels. In total, 314 cases of incident cardiovascular disease (CVD) (myocardial infarction, unstable angina, arterial revascularization, stroke, or cardiovascular death) were compared to age- and gender-matched controls. Conditional logistic regression models adjusting for risk factors evaluated associations between HDL-related biomarkers and incident CVD.

RESULTS

Cholesterol efflux capacity was moderately correlated with HDL cholesterol, apolipoprotein A-I, and HDL particle number (Spearman r= 0.39, 0.48, and 0.39 respectively; P<0.001). Baseline HDL particle number was inversely associated with incident CVD (adjusted odds ratio per SD increment [OR/SD], 0.69; 95% confidence interval [CI], 0.56-0.86; P<0.001), whereas no significant association was found for baseline cholesterol efflux capacity (OR/SD, 0.89; 95% CI, 0.72-1.10; P=0.28), HDL cholesterol (OR/SD, 0.82; 95% CI, 0.66-1.02; P=0.08), or apolipoprotein A-I (OR/SD, 0.83; 95% CI, 0.67-1.03; P=0.08). Twelve months of rosuvastatin (20 mg/day) did not change cholesterol efflux capacity (average percentage change -1.5%, 95% CI, -13.3 to +10.2; P=0.80), but increased HDL cholesterol (+7.7%), apolipoprotein A-I (+4.3%), and HDL particle number (+5.2%). On-statin cholesterol efflux capacity was inversely associated with incident CVD (OR/SD, 0.62; 95% CI, 0.42-0.92; P=0.02), although HDL particle number again emerged as the strongest predictor (OR/SD, 0.51; 95% CI, 0.33-0.77; P<0.001).

CONCLUSIONS

In JUPITER, cholesterol efflux capacity was associated with incident CVD in individuals on potent statin therapy but not at baseline. For both baseline and on-statin analyses, HDL particle number was the strongest of 4 HDL-related biomarkers as an inverse predictor of incident events and biomarker of residual risk.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00239681.

Effects of the cholesteryl ester transfer protein inhibitor, TA-8995, on cholesterol efflux capacity and high-density lipoprotein particle subclasses

BACKGROUND

TA-8995 is a potent inhibitor of cholesteryl ester transfer protein (CETP) with beneficial effects on lipids and lipoproteins. The effect of TA-8995 on cholesterol efflux capacity (CEC), a measure of high-density lipoprotein (HDL) function, and HDL subparticle distribution is largely unknown.

OBJECTIVE

To assess the effect of the CETP inhibitor TA-8995 on ABCA1- and non-ABCA1-driven CEC and on HDL particle distribution.

METHODS

Total, non-ABCA1-, and ABCA1-specific CEC from J774 cells and HDL subclass distribution assessed by two-dimensional gel electrophoresis were measured at baseline and after 12-week treatment in 187 mild-dyslipidemic patients randomized to placebo, 1 mg, 5 mg, 10 mg TA-8995, or 10 mg TA-8995 combined with 10 mg rosuvastatin (NCT01970215).

RESULTS

Compared with placebo, total, non-ABCA1-, and ABCA1-specific CEC were increased dose dependently by up to 38%, 72%, and 28%, respectively, in patients randomized to 10 mg of TA-8995. PreBeta-1 HDL, the primary acceptor for ABCA1-driven cholesterol efflux, was increased by 36%. This increase in preBeta-1 HDL correlated significantly with the total and the ABCA1-driven CEC increase, whereas the high-density lipoprotein cholesterol (HDL-C) increase did not.

CONCLUSION

TA-8995 dose dependently increased not only total and non-ABCA1-specific CEC but also ABCA1-specific CEC and preBeta-1 HDL particle levels. These findings suggest that TA-8995 not only increases HDL-C levels but also promotes functional properties of HDL particles. This CETP inhibitor-driven preBeta-1 HDL increase is an important predictor of both ABCA1 and total CEC increase, independent of HDL-C increase. Whether these changes in HDL particle composition and functionality have a beneficial effect on cardiovascular outcome requires formal testing in a cardiovascular outcome trial.

Cholesterol Efflux Capacity and Pre-Beta-1 HDL Concentrations Are Increased in Dyslipidemic Patients Treated With Evacetrapib

BACKGROUND

Potent cholesteryl ester transfer protein (CETP) inhibitors have been shown to substantially increase high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I levels as monotherapy and combined with statins. However, data on the effects of this class of drugs on macrophage cholesterol efflux capacity (CEC), a functional assay that characterizes a key step in the process of reverse cholesterol transport, are limited.

OBJECTIVES

This study assessed the impact of evacetrapib, statins, or combination therapy on CEC.

METHODS

We analyzed samples from 377 subjects with elevated low-density lipoprotein cholesterol (LDL-C) or low HDL-C levels who were enrolled in a phase 2 trial of evacetrapib. Percent changes from baseline in CEC (total, non-ABCA1-, and ABCA1-specific) and HDL subpopulations were evaluated after 12 weeks of treatment with placebo, statin monotherapy, evacetrapib monotherapy, or evacetrapib combined with statins. Pre-beta-1 HDL levels were quantified by immunofixation and nondenaturing 2-dimensional gel electrophoresis (2DGE).

RESULTS

Relative to placebo, evacetrapib monotherapy increased dose-dependent total and non-ABCA1-specific CEC up to 34% and 47%, respectively. Evacetrapib monotherapy also increased ABCA1-specific CEC up to 26%. Relative to statin monotherapy, evacetrapib with statins also increased total, non-ABCA1-, and ABCA1-specific CEC by 21%, 27%, and 15%, respectively. In contrast, rosuvastatin and simvastatin significantly reduced total and ABCA1-specific CEC, whereas atorvastatin had no significant effect. Consistent with ABCA1-specific CEC, evacetrapib monotherapy and evacetrapib combined with statins significantly increased pre-beta-1 HDL levels as measured by either method.

CONCLUSIONS

Evacetrapib, as monotherapy and combined with statins, not only increased total CEC, but also increased ABCA1-specific CEC and pre-beta-1 HDL. The mechanisms by which potent CETP inhibition increases ABCA1-specific CEC and pre-beta-1 HDL require further study. (A Study of LY2484595 in Patients With High LDL-C or Low HDL-C; NCT01105975).

L-Carnitine intake and high trimethylamine N-oxide plasma levels correlate with low aortic lesions in ApoE(-/-) transgenic mice expressing CETP

OBJECTIVE

Dietary l-carnitine can be metabolized by intestinal microbiota to trimethylamine, which is absorbed by the gut and further oxidized to trimethylamine N-oxide (TMAO) in the liver. TMAO plasma levels have been associated with atherosclerosis development in ApoE(-/-) mice. To better understand the mechanisms behind this association, we conducted in vitro and in vivo studies looking at the effect of TMAO on different steps of atherosclerotic disease progression.

METHODS

J774 mouse macrophage cells were used to evaluate the effect of TMAO on foam cell formation. Male ApoE(-/-) mice transfected with human cholesteryl ester transfer protein (hCETP) were fed l-carnitine and/or methimazole, a flavin monooxygenase 3 (FMO3) inhibitor that prevents the formation of TMAO. Following 12 week treatment, l-carnitine and TMAO plasma levels, aortic lesion development, and lipid profiles were determined.

RESULTS

TMAO at concentrations up to 10-fold the Cmax reported in humans did not affect in vitro foam cell formation. In ApoE(-/-)mice expressing hCETP, high doses of l-carnitine resulted in a significant increase in plasma TMAO levels. Surprisingly, and independently from treatment group, TMAO levels inversely correlated with aortic lesion size in both aortic root and thoracic aorta. High TMAO levels were found to significantly correlate with smaller aortic lesion area. Plasma lipid and lipoprotein levels did not change with treatment nor with TMAO levels, suggesting that the observed effects on lesion area were independent from lipid changes.

CONCLUSION

These findings suggest that TMAO slows aortic lesion formation in this mouse model and may have a protective effect against atherosclerosis development in humans.

Increased plasma cholesterol esterification by LCAT reduces diet-induced atherosclerosis in SR-BI knockout mice

LCAT, a plasma enzyme that esterifies cholesterol, has been proposed to play an antiatherogenic role, but animal and epidemiologic studies have yielded conflicting results. To gain insight into LCAT and the role of free cholesterol (FC) in atherosclerosis, we examined the effect of LCAT over- and underexpression in diet-induced atherosclerosis in scavenger receptor class B member I-deficient [Scarab(-/-)] mice, which have a secondary defect in cholesterol esterification. Scarab(-/-)×LCAT-null [Lcat(-/-)] mice had a decrease in HDL-cholesterol and a high plasma ratio of FC/total cholesterol (TC) (0.88 ± 0.033) and a marked increase in VLDL-cholesterol (VLDL-C) on a high-fat diet. Scarab(-/-)×LCAT-transgenic (Tg) mice had lower levels of VLDL-C and a normal plasma FC/TC ratio (0.28 ± 0.005). Plasma from Scarab(-/-)×LCAT-Tg mice also showed an increase in cholesterol esterification during in vitro cholesterol efflux, but increased esterification did not appear to affect the overall rate of cholesterol efflux or hepatic uptake of cholesterol. Scarab(-/-)×LCAT-Tg mice also displayed a 51% decrease in aortic sinus atherosclerosis compared with Scarab(-/-) mice (P < 0.05). In summary, we demonstrate that increased cholesterol esterification by LCAT is atheroprotective, most likely through its ability to increase HDL levels and decrease pro-atherogenic apoB-containing lipoprotein particles.

Abstract 238: Incubation of MDCO216 With Human Serum or Plasma Potentiates ABCA1-Mediated Cholesterol Efflux Capacity, Increases Prebeta-1 HDL and Causes a Shift From Small to Large Alpha HDL Particles

MDCO216 is a complex of dimeric apoA-IMilano and POPC, shown to reduce atherosclerotic plaque burden. Here we studied the effect of incubation of human plasma or serum with MDCO216 on cholesterol efflux capacity from J774 cells, on prebeta-1 HDL and various HDL subfractions. At clinically relevant concentrations MDCO216 by itself markedly stimulates global and ABCA1-mediated cholesterol efflux. When incubated with human serum a time-dependent synergistic increase of the ABCA1 mediated efflux capacity is observed. Using the Sekisui ELISA for prebeta-1 HDL, MDCO216 itself is poorly detected. Prebeta-1 HDL is rapidly lost when human plasma alone is incubated at 37 o C. However, incubation of human plasma with MDCO216 at 37 o C causes a robust generation of new prebeta-1 HDL. 2D-Electrophoresis followed by immunoblotting with a general apoA-I antibody that also detects apoA-IM confirms the increase in prebeta-1 HDL (having a different mobility than pure MDCO216 particles), and shows a concomitant disappearance of alpha-3 HDL, alpha-4 HDL and MDCO216, and an increase in alpha-1 and alpha-2 HDL. NMR analysis of plasma incubated with MDCO216 at 47 o C confirms very rapid disappearance of small HDL and increase of medium and large HDL particles. In conclusion, incubation of human plasma or serum with MDCO216 strongly enhances ABCA1-mediated cholesterol efflux capacity, causes a strong increase of prebeta-1 HDL and drastically changes HDL subfraction distribution, consistent with anti-atherosclerotic activity.

Effect of repeated apoA-IMilano/POPC infusion on lipids, (apo)lipoproteins, and serum cholesterol efflux capacity in cynomolgus monkeys

MDCO-216, a complex of dimeric recombinant apoA-IMilano (apoA-IM) and palmitoyl-oleoyl-phosphatidylcholine (POPC), was administered to cynomolgus monkeys at 30, 100, and 300 mg/kg every other day for a total of 21 infusions, and effects on lipids, (apo)lipoproteins, and ex-vivo cholesterol efflux capacity were monitored. After 7 or 20 infusions, free cholesterol (FC) and phospholipids (PL) were strongly increased, and HDL-cholesterol (HDL-C), apoA-I, and apoA-II were strongly decreased. We then measured short-term effects on apoA-IM, lipids, and (apo)lipoproteins after the first or the last infusion. After the first infusion, PL and FC went up in the HDL region and also in the LDL and VLDL regions. ApoE shifted from HDL to LDL and VLDL regions, while ApoA-IM remained located in the HDL region. On day 41, ApoE levels were 8-fold higher than on day 1, and FC, PL, and apoE resided mostly in LDL and VLDL regions. Drug infusion quickly decreased the endogenous cholesterol esterification rate. ABCA1-mediated cholesterol efflux on day 41 was markedly increased, whereas scavenger receptor type B1 (SRB1) and ABCG1-mediated effluxes were only weakly increased. Strong increase of FC is due to sustained stimulation of ABCA1-mediated efflux, and drop in HDL and formation of large apoE-rich particles are due to lack of LCAT activation.

Abstract 111: A Novel Assay that Incorporates Measurement of Ex Vivo LCAT Activity with Measurement of Cholesterol Efflux Capacity - Assessment of Two Biomarkers of Serum HDL Function

Atheroprotective properties of high-density lipoproteins (HDL) may be due to the ability to remove lipids from peripheral cells to the liver for excretion during reverse cholesterol transport (RCT). Assays that measure functionality of serum HDL are needed to evaluate the therapeutic potential of treatments targeting HDL metabolism. Recent work shows an inverse correlation between cholesterol efflux capacity of serum HDL and coronary artery disease, demonstrating the value of measuring HDL functionality. Another function of HDL that promotes RCT is the capacity for esterification of cholesterol by lecithin:cholesterol acyltransferase (LCAT). A novel assay was developed that in addition to measurement of serum HDL efflux capacity incorporates measuring the capacity for esterification of HDL-cholesterol by LCAT. Assay methodology includes measurement of global cholesterol efflux via all known pathways (ABCA1, SR-BI, ABCG1 and passive diffusion) from J774 macrophage cells to serum HDL, and measurement of the proportion of cholesterol transferred to serum HDL that is esterified by LCAT over 4h. Assay validation included assessment of intra-assay repeatability, inter-assay precision, linearity, LOQ and specificity. Results showed the intra-assay variability (%CV) from six independent preparations of serum HDL is ≤10% for both the % efflux and the % esterification of cholesterol. Inter-assay variability between four separate assays is ≤13% for both the % efflux and the % esterification of cholesterol. Cholesterol efflux is linear up to concentrations of 2.8% serum HDL and cholesterol esterification is linear up to concentrations of 4% serum. The LOQ for the assay is 0.15% cholesterol efflux and 0.40% cholesterol esterification. Global cholesterol efflux was determined to be specific for known cholesterol acceptors such as serum HDL (p≤0.0001 versus media blank). The cholesterol esterification measured was determined to be specific for the action of LCAT because the presence of LCAT inhibitor decreased the % ester by 86-97% (p≤0.0009). This novel assay allows the measurement of two functional aspects of an individual subject’s serum HDL, the capacities for both cholesterol efflux and for esterification of cholesterol by LCAT.

The impact of partial and complete loss-of-function mutations in endothelial lipase on high-density lipoprotein levels and functionality in humans

BACKGROUND

Endothelial lipase is a phospholipase with activity against high-density lipoprotein. Although a small number of mutations in LIPG have been described, the role of LIPG in protection against atherosclerosis is unclear.

METHODS AND RESULTS

We identified 8 loss-of-function (LOF) mutations in LIPG in individuals with high-density lipoprotein cholesterol. Functional analysis confirmed that most rare mutations abolish lipase activity in vitro, indicating complete LOF, whereas 2 more common mutations N396S and R476W reduce activity by ≈50%, indicating partial LOF and implying ≈50% and ≈75% remaining endothelial lipase function in heterozygous complete LOF and partial LOF mutation carriers, respectively. complete LOF mutation carriers had significantly higher plasma high-density lipoprotein cholesterol levels compared with partial LOF mutation carriers. Apolipoprotein B-depleted serum from complete LOF carriers showed significantly enhanced cholesterol efflux acceptor capacity, whereas only trends were observed in partial LOF carriers. Carriers of LIPG mutations exhibited trends toward reduced coronary artery disease in 4 independent cohorts (meta-analysis odds ratio, 0.7; P=0.04).

CONCLUSIONS

Our data suggest that the impact of LIPG mutations is directly related to their effect on endothelial lipase function and support that antagonism of endothelial lipase function improves cardioprotection.

Abstract 288: An Improved Method for the Isolation of HDL from Human Serum

In an effort to reduce the time and labor resources required for the standard HDL isolation protocol using sequential ultracentrifugation, our laboratory has investigated a modified process for isolation of HDL from human serum. Our method employs an alternative step for removing VLDL and LDL from human serum that requires less than one hour and replaces the first 18 hour ultracentrifugation step. This alternative process is based on the well documented ability of polyethylene glycol (PEG) to selectively and irreversibly precipitate apolipoprotein B-containing lipoproteins. Subsequently, both methods then use a 21 hour ultracentrifugation spin to separate HDL from all other non-lipoprotein components of human serum. For this study comparing the methods, 1.5 ml of human serum was used. The human serum starting material had a total cholesterol value of 262 mg/dL with the following lipoprotein cholesterol profile: 178 mg/dL LDL-C (68%), 34 mg/dL VLDL-C (13%) and HDL-C 48 mg/dL (18%). Comparison of the two methods demonstrates similar recovery of HDL-C from human serum, 35% vs 37% for the standard method versus modified method, respectively. The total cholesterol recovered using the standard protocol was slightly higher than the modified method. However, as shown by lipoprotein gel electrophoresis, HDL isolated by the standard method was only 80% pure, with 20% of the cholesterol present as VLDL and LDL contaminants remaining in the preparation. In contrast, using our modified process, isolated HDL was >99% pure with no detectable VLDL or LDL cholesterol present. In summary, our laboratory has developed a methodology for the isolation of HDL from human serum that: 1) requires substantially less time and resources, 2) provides the same recovery of HDL-C from serum as the standard method and 3) provides a higher purity HDL than is achieved from the standard sequential ultracentrifugation method.

Control of chronic inflammation with pathway selective estrogen receptor ligands

The discovery of novel intervention points in the inflammatory pathway has been a focus of drug development in recent years. We have identified pathway selective ligands for the estrogen receptor (ER) that inhibit NF-kappaB mediated inflammatory gene expression causing a reduction of cytokines, chemokines, adhesion molecules and inflammatory enzymes. SAR development of a series of 4-(Indazol-3-yl)-phenols has led to the identification of WAY-169916 an orally active non-steroidal ligand with the potential use in the treatment of inflammatory diseases without the classical proliferative effects associated with non-selective estrogens.

Differential estrogen receptor gene expression in human peripheral blood mononuclear cell populations

Estrogens have been shown to modulate immune responses. Several studies have demonstrated the capacity of T cells, B cells, and monocytes to respond to estrogens and estrogen receptor (ER) expression in these cell types has been reported. However, little is known regarding the relative expression in these cells of ERalpha and the more recently identified ERbeta. In the present study, results of quantitative TaqMan RT-PCR analyses indicate that ERs are differentially expressed in PBMC subsets. CD4+ T cells express relatively high levels of ERalpha mRNA compared with ERbeta, whereas B cells express high levels of ERbeta mRNA but low levels of ERalpha. Peripheral blood CD8+ T cells and monocytes express low but comparable levels of both ERs. This quantitative analysis of ER expression in distinct PBMC subsets may provide a basis for dissecting the mechanisms of immune modulation by estrogens and identifying therapeutic targets for the treatment of inflammatory and immunologic disorders.

Suppression of experimental autoimmune encephalomyelitis using estrogen receptor-selective ligands

Estrogens have been shown to modulate disease activity in experimental autoimmune encephalomyelitis (EAE), the mouse model for multiple sclerosis. Consistent with these findings, the severity of disease is reduced in pregnant women with multiple sclerosis when levels of estrogens are high. Estrogens bind to two known estrogen receptors (ER), ERalpha and ERbeta. The relative contribution of these receptors to estrogen-mediated suppression of EAE was explored using ER-selective ligands. The ER antagonist ICI 182 780 reversed the suppressive effects of 17beta-estradiol (E2), demonstrating that the protective effects of E2 on disease are dependent upon ER signaling. Treatment of SJL mice with the ERalpha-selective agonist proteolipid protein (PPT) prior to the induction of disease resulted in suppression of clinical symptoms of disease, whereas treatment with an ERbeta-selective agonist (WAY-202041) had no effect. Treatment of mice with PLP peptide 139-151 (PPT) was also associated with decreased immune responses associated with disease. Consistent with its lack of effect on disease, the ERbeta agonist had minimal effects on immune responses. The use of selective estrogen receptor modulators (SERMs) in this model was also explored, and we show that raloxifene and WAY-138923 were also effective in suppressing disease. These results demonstrate the beneficial effects of estrogen receptor ligands, in particular ERalpha-selective ligands, and may have implications in the development of therapeutic strategies for multiple sclerosis.

Future therapies for the prevention and treatment of venous and arterial thrombosis

The incidence of thrombosis as a complication of invasive surgery, in cancer patients, as a cause or complication of stroke, acute myocardial infarction (AMI), thrombolysis, unstable angina (UA) or angioplasty is substantial. To better serve this patient population in the prevention and prophylaxis of thrombosis, new types of anticoagulant drugs are under development by the pharmaceutical industry. The goal of these efforts are orally-active anticoagulants with specificity and pharmacokinetic properties that could translate into better control of anticoagulation and thrombosis and less bleading liability compared to the currently used anticoagulants: heparin, the low molecular weight heparins and warfarin. Various approaches for which there is a great deal of activity include: tissue factor/Factor VIIa inhibitors, Factor Xa inhibitors, thrombin inhibitors, glycoprotein IIb/IIIa antagonists. There is also interest in Factor IXa inhibitors, thrombin receptor antagonists and inhibitors of plasminogen activator inhibitor-1.

Identification of pathway-selective estrogen receptor ligands that inhibit NF-kappaB transcriptional activity

Inflammation is now recognized as a key component in a number of diseases such as atherosclerosis, rheumatoid arthritis, and inflammatory bowel disease. The transcription factor NF-kappaB has been shown to be involved in both the early and late stages of the inflammatory-proliferative process. In this report, we describe the identification of the pathway-selective estrogen receptor (ER) ligand, WAY-169916, that inhibits NF-kappaB transcriptional activity but is devoid of conventional estrogenic activity. This pathway-selective ligand does not promote the classic actions of estrogens such as stimulation of uterine proliferation or ER-mediated gene expression, but is a potent antiinflammatory agent, as demonstrated in the HLA-B27 transgenic rat model of inflammatory bowel disease. Our results indicate the potential utility of pathway-selective ER ligands such as WAY-169916 in the treatment of chronic inflammatory diseases.

Design, Synthesis, and Biological Evaluation of Thio-Containing Compounds with Serum HDL-Cholesterol-Elevating Properties

A novel series of substituted sulfanyldihydroimidazolones (1) that modulates high-density lipoprotein cholesterol (HDL-C) has been reported to have HDL-elevating properties in several animal models. Concerns about the chemical and metabolic stability of 1 directed us to explore the structure-activity relationship (SAR) of a related series of substituted thiohydantoins (2). Expansion of the scope of the thiohydantoin series led to exploration of compounds in related thio-containing ring systems 3-7 and the N-cyanoguanidine derivative 8. Compounds were tested sequentially in three animal models to assess their HDL-C elevating efficacy and safety profiles. Further evaluation of selected compounds in a dose-response paradigm culminated in the identification of compound 2.39 as a candidate compound for advanced preclinical studies.

Effect of sirolimus on the cholesterol content of aortic arch in ApoE knockout mice

Chronic inflammatory responses involving the immune system have been implicated in the process of atherosclerosis. Sirolimus (Rapamycin, Rapamune), a potent immunosuppressant used to prevent rejection of transplanted kidneys, has also proven effective at inhibiting restenosis in humans when eluted from implanted stents. The aim of this study was to evaluate the effect of sirolimus treatment on the development of atherosclerosis in the aortic arch of apo E-/- mice fed a high-fat (Western) diet. Following 12 weeks of treatment with sirolimus (4 mg/kg/d), the cholesterol content of the arch was reduced by 36% compared to untreated control mice fed the Western diet only. Although the murine model is not comparable to the human situation, the results of this study suggest that sirolimus may exert beneficial effects on atherosclerosis in transplant patients.

Protective effect of the immunosuppressant sirolimus against aortic atherosclerosis in apo E-deficient mice

Atherosclerosis is a chronic inflammatory disease that develops in response to injury to the vessel wall, and is augmented by hypercholesterolemia. To further delineate the role of the immune system and local factors in this process, we assessed the effects of the immunosuppressant sirolimus (Rapamycin, RAPAMUNE, Wyeth, Collegeville, PA) on atherosclerosis in the apoE-deficient (apoE KO) mouse, a well-accepted model of cardiovascular disease. ApoE KO mice were fed a high fat diet and sirolimus was administered. After 12 weeks, atherosclerotic lesions and plasma lipoproteins were measured. The expression of cytokines associated with atherosclerosis was also examined. All groups demonstrated plasma total cholesterol (TC) >1100 mg/dL. Sirolimus treatment was associated with a 30% increase in LDL-cholesterol (LDLc) and a dose-dependent elevation in HDL-cholesterol (HDLc). Despite increased LDLc, aortic atherosclerosis was markedly reduced in all sirolimus-treated groups. Sirolimus treatment resulted in decreased expression of IL-12p40, IFN-gamma and IL-10 mRNA. In contrast, TGF-beta1 was elevated. Sirolimus significantly reduced atherosclerosis in apo E-KO mice; this effect is independent of, and obviates, elevated plasma TC and LDLc. Sirolimus might therefore be of benefit on atherosclerosis in patients undergoing therapy, independent of any impact on circulating lipids.

Estrogen receptors alpha and beta have similar activities in multiple endothelial cell pathways

The presence of both estrogen receptor alpha (ERalpha) and ERbeta in vascular cells has greatly increased the complexity of potential estrogen regulatory pathways in the cardiovascular system. Here, human umbilical vein endothelial cells were engineered using adenovirus vectors to express either ERalpha or ERbeta. The activities of ERalpha and ERbeta were compared in three distinct gene regulatory pathways, including inhibition of IL-1beta induction of E-selectin expression, inhibition of basal endothelin-1 production, and the ability to induce two matrix-stabilizing enzymes: tissue transglutaminase and a novel member of the lysyl oxidase family. Both ERs were active on these end points, although ERbeta was typically less efficacious than ERalpha. As no class of gene regulation could differentiate ERalpha from ERbeta activity, we characterized a novel steroid (7alpha-thiophenyl-E2) that bound with similar affinities to ERalpha and ERbeta, but functioned as an ERalpha agonist and ERbeta antagonist for all of these endothelial responses. This pattern of receptor subtype-selective activity was not unique to endothelial cells, but was also seen in metabolically active HepG2 cells, suggesting potential in vivo utility. The panel of endothelial responses coupled with a selective modulator should provide a means to characterize the roles of ERalpha and ERbeta in endothelial cells in vivo.

Twenty-eight-day efficacy and phamacokinetics of the sirolimus-eluting stent

BACKGROUND

In-stent restenosis is caused by neointimal hyperplasia. Sirolimus (rapamycin; Wyeth Research, Radnor, Pennsylvania, USA) inhibits vascular smooth muscle cell proliferation and we evaluated the efficacy of sirolimus in reducing neointimal formation in a rabbit iliac model and in-vivo pharmacokinetics in the porcine coronary model.

DESIGN

Randomized, blinded, prospective animal study.

METHODS

Bilateral rabbit iliac artery stent implantation was performed using crossflex stents (Cordis Corporation, Warren, New Jersey, USA) coated with sirolimus incorporated in a nonerodable polymer. Arteries were randomized to one of four stent groups: uncoated stents (n = 8); polymer control stents (n = 10); low-dose sirolimus-eluting stents (n = 9); and high-dose sirolimus-eluting stents (n = 10). Histomorphometry was performed at 28 days. Arterial tissue and stents were retrieved at 8, 14 and 28 days and blood samples were obtained daily during the first week.

RESULTS

Treatment with low-dose sirolimus was associated with a 23% (P = NS) reduction in neointimal area and treatment with high-dose sirolimus with a 45% (P < 0.05) reduction. Sustained drug release from the stent and prolonged intramural arterial deposition were confirmed for up to 28 days. No detectable sirolimus was found in the blood after 2 days.

CONCLUSION

Controlled-release local delivery of a cell-cycle inhibitor from a nonerodable polymer-coated stent reduced neointimal formation in rabbit iliac arteries in a dose-dependent manner and represents a promising strategy for preventing restenosis.

Reciprocal antagonism between estrogen receptor and NF-kappaB activity in vivo

The functional interaction, or "cross-talk," between estrogen receptor (ER) and the proinflammatory transcription factor nuclear factor (NF)-kappaB demonstrated in vitro has been suggested to play a role in estrogen prevention of cardiovascular disease. Here, we demonstrate that this reciprocal cross-talk occurs in vivo. Ovariectomized C57BL/6 mice fed an atherogenic diet had increased hepatic levels of active NF-kappaB and numerous inflammatory genes, including MHC invariant chain (Ii), vascular cell adhesion molecule-1, tumor necrosis factor-alpha, and RANTES. Treatment with 17alpha-ethinylestradiol (EE) strongly blocked induction of these genes but had no effect on their basal expression levels. ER was required for this activity, because the antagonist ICI 182,780 completely blocked the inhibitory activity of EE. Gene activation by EE was not required for inhibition of inflammatory gene expression, because both the phytoestrogen genistein and low doses of EE were effective in blocking inflammatory gene induction without inducing marker genes such as intestinal trefoil factor (ITF) or myo-inositol-1-phosphate synthase (IPS). The in vivo transcriptional interference was reciprocal, with EE induction of ITF and IPS greatly reduced in animals fed the atherogenic diet versus chow-fed controls. This interference was specific to the liver, because diet had no effect on uterine weight increases produced by EE. Transfection experiments confirmed that the extent of inhibition of ER-mediated transcription by inflammatory stimuli correlated with the extent of NF-kappaB activation. These results suggest that the cross-talk between ER and NF-kappaB does occur in vivo and may indeed contribute significantly to the cardioprotective effects of estrogen.

The role of CBP in estrogen receptor cross-talk with nuclear factor-kappaB in HepG2 cells

Functional interactions or cross-talk between ligand-activated nuclear receptors and the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) may play a major role in ligand-mediated modification of diseases processes. In particular, the cardioprotective effects of estrogen replacement therapy are thought to be due in part to the ability of ligand-bound estrogen receptor (ER) to inhibit NF-kappaB function. In the current study 17beta-estradiol-bound ERalpha interfered with cytokine-induced activation of a NF-kappaB reporter in HepG2 cells. The estrogen metabolite, 17alpha-ethinyl estradiol, and the phytoestrogen, genistein, were also effective inhibitors of NF-kappaB activation, whereas tamoxifen, 4-hydroxytamoxifen, and raloxifene were inactive. This inhibition was reciprocal, as NF-kappaB interfered with the trans-activation properties of ERalpha. Ligand-bound ERalpha did not inhibit NF-kappaB binding to DNA, but it did decrease the histone acetyltransferase activity required for NF-kappaB transcriptional activity. Coexpression of the transcription coactivator CREB binding protein (CBP), but not steroid receptor coactivator 1a, reversed the ERalpha-mediated inhibition of NF-kappaB activity. Mammalian two-hybrid experiments also revealed that ligand-bound ERalpha can interact functionally with CBP-NF-kappaB complexes. We suggest that CBP targeting by ERalpha results in the inhibition of NF-kappaB and may occur through formation of transcriptionally inert multimeric complexes that are dependent upon the nature of the ERalpha ligand.

Effects of 17 alpha-dihydroequilenin sulfate on atherosclerotic male and female rhesus monkeys

OBJECTIVES

Our purpose was to determine the effects of 17 alpha-dihydroequilenin on plasma lipid and lipoprotein, glucose, and insulin concentrations; coronary artery vasomotor function; and reproductive organ and mammary gland proliferation in atherosclerotic male and female rhesus macaques.

STUDY DESIGN

Fifty adult female and 33 adult male rhesus macaques were randomized to treatment by lifetime dietary cholesterol exposure and ratio of total plasma cholesterol to high-density lipoprotein cholesterol. The female treatment groups were intact female controls (n = 9), ovariectomized controls (n = 16), ovariectomized plus 0.3 mg/kg/day 17 alpha-dihydroequilenin (n = 17) and ovariectomized plus subcutaneous estradiol (n = 7). The male treatment groups were control (n = 16) and 1.25 mg/kg/day 17 alpha-dihydroequilenin (n = 17). Treatment lasted 5 weeks. Longitudinal assessments of plasma lipid and lipoprotein and glucose and insulin concentrations were performed. Coronary artery vasomotor function was assessed by quantitative coronary angiography 1 week after initiation of treatment. Morphologic and immunohistochemical assessments of proliferation index values of reproductive organs and mammary glands were done at necropsy.

RESULTS

17 alpha-Dihydroequilenin prevented endothelium-dependent vasoconstriction in males (p < 0.05) and ovariectomized females (p < 0.08). 17 alpha-Dihydroequilenin treatment increased plasma apolipoprotein A-1 concentrations (p < 0.05) and lowered fasting insulin concentrations (p < 0.05) without changing fasting plasma glucose concentrations in males. 17 alpha-Dihydroequilenin had no other effects on plasma lipid and lipoprotein concentrations in either males or females. It had no trophic effects on uterus, endometrium, or breast. There was no effect on either prostatic or testicular weight.

CONCLUSION

17 alpha-Dihydroequilenin may represent a single-agent hormone therapy for reduction of ischemic hear disease risk for both menopausal women and men. It has no apparent trophic effects on reproductive organs or mammary glands of female and male rhesus macaques.

In vitro antioxidant effects of estrogens with a hindered 3-OH function on the copper-induced oxidation of low density lipoprotein

Estrogens with some bulky alkyl substituents in both the 2- and 4-positions have been synthesized and evaluated for the ability to inhibit the in vitro oxidation of low density lipoprotein as determined by the thiobarbituric reactive substances method. The present compounds with bulky groups in either the 2- or the 4-position (but not both the 2- and 4-) were especially effective as antioxidants, having IC50 values lower than either estradiol or probucol; however, they do not bind to the estrogen receptor with any great affinities (RBA < 0.1 versus estradiol). This separation of antioxidant efficacy from estrogenicity may allow these compounds to serve as useful probes for ascertaining the relative importance of these effects in the cardioprotective role played by estrogens.

Determination of 17 alpha-dihydroequilenin in rat, rabbit and monkey plasma by high-performance liquid chromatography with fluorimetric detection

A high-performance liquid chromatographic (HPLC) method with fluorescence detection for the determination of total (unconjugated and conjugated) 17 alpha-dihydroequilenin in male and female rat, female rabbit and male and female rhesus monkey plasma is described here. Plasma sample preparation involved hydrolysis with enzyme (Glusulase), addition of internal standard (14 beta-equilenin) and solvent extraction. The extracts were chromatographed on a C6, 5-microns reversed-phase HPLC column and detection was accomplished with a fluorescence detector operated at an excitation wavelength of 210 nm and an emission wavelength of 370 nm. The assay was linear over a range of 2.5 to 100 ng/ml in male and female rat plasma, and 5 to 500 ng/ml in female rabbit and male and female monkey plasma. The method was specific, accurate and reproducible (percent differences < 14.5; coefficients of variation < 9.5%) in all matrices examined. The applicability of this method was successfully tested by quantifying total plasma concentrations of 17 alpha-dihydroequilenin in ovariectomized female rats, ovariectomized female rabbits and a normal female rhesus monkey receiving 2.0, 8.3 and 0.1 mg/kg, respectively, of 17 alpha-dihydroequilenin sulfate intragastrically.

Effect of 17 alpha-dihydroequilin sulfate, a conjugated equine estrogen, and ethynylestradiol on atherosclerosis in cholesterol-fed rabbits

The effect of 17 alpha-dihydroequilin sulfate (DHES), a water-soluble estrogen of conjugated estrogens (Premarin), and ethynylestradiol (EE), a commonly used estrogen found in many oral contraceptives, on the development of atherosclerosis was studied in rabbits fed an atherogenic diet (0.2% cholesterol) for 24 weeks. Ten animals were given 15 micrograms. kg-1.d-1 EE, 10 received 3.8 mg.kg-1.d-1 of DHES, and the remaining 10 sham-ovariectomized and 10 ovariectomized animals served as cholesterol-fed controls. These doses were chosen to have similar estrogenic potency. Plasma cholesterol concentrations increased to about 900 mg/dL and did not differ among the experimental groups. After 24 weeks, plasma beta-VLDL and HDL cholesterol concentrations were the same for all cholesterol-fed groups, while LDL cholesterol was significantly higher in the two estrogen-treated groups. In spite of this, both EE and DHES significantly reduced atherosclerosis by 35% in the aortic arch and 75% to 80% in the thoracic and abdominal aorta. The reduction in atherosclerosis was seen in animals with a wide range (400 to 1400 mg/dL) of plasma cholesterol concentrations and was independent of lipoprotein profile. beta-VLDL isolated from estrogen-treated animals was not significantly different from control beta-VLDL in its ability to stimulate cholesterol accumulation in THP-1 macrophages in culture. This suggests that the protective effect of estrogens on the development of atherosclerosis is not mediated by qualitative differences in beta-VLDL that affect uptake by macrophages. The results of this study extend our knowledge of the range of estrogens that reduce atherosclerosis. Given the lack of effect on plasma lipid and lipoprotein concentrations, these data are consistent with the conclusion that estrogens exert some of this beneficial effect directly at the level of the arterial wall by influencing certain key components in the pathogenesis of atherosclerosis.

A conjugated equine estrogen with differential effects on uterine weight and plasma cholesterol in the rat

OBJECTIVE

Our purpose was to determine the effect of Premarin (conjugated estrogens) and three of its component estrogens on uterine weight and plasma cholesterol concentrations in surgically menopausal female rats.

STUDY DESIGN

A randomized trial of Premarin and three component estrogens--estrone sulfate, 17 alpha-estradiol sulfate, and 17 alpha-dihydroequilenin sulfate--in female rats after oophorectomy.

RESULTS

High-dose Premarin and high- and middle-dose estrone sulfate significantly increased uterine weight relative to untreated controls (high-dose Premarin, 243.34 +/- 0.15 mg; high-dose estrone sulfate, 376.1 +/- 9.36 mg; middle-dose estrone sulfate, 249.0 +/- 6.34 mg; untreated controls, 124.63 +/- 3.17 mg; for all, p < 0.05). 17 alpha-Dihydroequilenin sulfate had no effect on uterine weight relative to controls. All 17 alpha-dihydroequilenin sulfate doses markedly reduced total plasma cholesterol concentrations versus controls (34.02 +/- 3.44 mg/dl, 32.49 +/- 1.08 mg/dl, and 71.55 +/- 5.16 mg/dl vs 90.44 +/- 1.06 mg/dl; for all, p < 0.02). 17 alpha-Dihydroequilenin sulfate had a more pronounced effect on low- or very-low-density lipoprotein cholesterol than total plasma cholesterol or high-density lipoprotein cholesterol concentrations.

CONCLUSIONS

17 alpha-Dihydroequilenin sulfate reduced total plasma cholesterol concentrations without inducing uterine growth in rats after oophorectomy.

Beta-VLDL metabolism by pigeon macrophages. Evidence for two binding sites with different potentials promoting cholesterol accumulation

Previous studies from our laboratory (J Lipid Res 1988;29:643-656) have shown that thioglycolate-elicited peritoneal macrophages from White Carneau and Show Racer pigeons, like mammalian macrophages, have on their surfaces specific receptors for acetylated low density lipoprotein (acLDL) and beta-migrating very low density lipoproteins (beta-VLDL). The binding kinetics of beta-VLDL were complex, however, suggesting more than one binding site. The purpose of the present study was to further characterize these beta-VLDL binding sites. Scatchard analysis of 125I-beta-VLDL binding curves indicated at least two classes of binding sites. The first binds pigeon beta-VLDL and LDL with high affinity (Kd approximately 7 micrograms/ml), is down-regulated by cholesterol loading, requires calcium, and is destroyed by the proteolytic enzyme, pronase. This pigeon beta-VLDL receptor is specific for pigeon beta-VLDL and LDL and does not recognize HDL, acLDL, methyl LDL, cynomolgus monkey LDL, or rabbit beta-VLDL. Like the mammalian macrophage beta-VLDL receptor, the "pigeon beta-VLDL receptor" has many of the characteristics of an LDL receptor. The second class of binding sites is relatively nonspecific, recognizing both pigeon and rabbit beta-VLDL, LDL, acLDL, methyl LDL, and HDL. Binding to this site is not altered by incubation of macrophages with pronase or by cholesterol loading. This binding site has low affinity for beta-VLDL (Kd approximately 100 micrograms/ml), but high capacity. We have called this the "lipoprotein binding site," a term used by others to describe similar lipoprotein binding characteristics on a variety of cells. Not only does binding to this site promote the internalization and degradation of lipoproteins, but it may also facilitate the independent uptake of cholesterol. This conclusion is based on the observation that more cholesterol accumulates in cells incubated with rabbit beta-VLDL, which binds only to the lipoprotein binding site, than can be accounted for by beta-VLDL uptake and degradation. Since the lipoprotein binding site recognizes a variety of normal, as well as abnormal, lipoproteins, it would not require the generation of abnormal lipoprotein products, as must occur with the scavenger receptor, to promote the accumulation of cholesteryl esters in macrophages of atherosclerotic lesions. This, coupled with the fact that the lipoprotein binding site is not down-regulated by cholesterol loading, suggests that it could provide an alternative mechanism to the scavenger receptor pathway for the formation of foam cells.

Lipoprotein metabolism by macrophages from atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons

The presence of specific receptors for the metabolism of acetylated low density lipoprotein (AcLDL) and beta-migrating very low density lipoprotein (beta-VLDL) was demonstrated in thioglycolate-elicited peritoneal macrophages from both atherosclerosis-susceptible White Carneau (WC) and resistant Show Racer (SR) pigeons. Macrophages from both breeds metabolized AcLDL through a single class of receptors that were similar, but not identical, to the scavenger receptors described in mammalian macrophages. Both pigeon and mammalian AcLDL bound to this receptor. At 37 degrees C, AcLDL was internalized and degraded in the lysosomes, and cholesterol esterification and cholesteryl ester accumulation were stimulated. As in mammalian macrophages, AcLDL receptor activity was not down-regulated by cholesterol loading. In contrast, AcLDL binding was poorly competed for by fucoidin or polyinosinic acid, and the magnitude of cholesteryl ester accumulation was only about one-half of that seen with mouse peritoneal macrophages. Pigeon beta-VLDL bound to both a high and a low affinity site on pigeon macrophages. Binding to the high affinity site was calcium-dependent, pronase-sensitive, and down-regulated by cholesterol loading. Cholesterol esterification and cholesteryl ester accumulation with beta-VLDL were stimulated to an equal or greater extent than with AcLDL. Unlike mammalian macrophages, the pigeon beta-VLDL receptor did not require apolipoprotein E, as evidenced by the lack of apoE in pigeon lipoproteins and by the failure of rabbit beta-VLDL, containing apoE, to compete for binding. Pigeon LDL, but not mammalian LDL, was recognized by the pigeon beta-VLDL receptor, suggesting that like the mammalian beta-VLDL receptor, the pigeon beta-VLDL receptor may be a form of an LDL receptor. This was an unexpected finding since pigeon fibroblasts and smooth muscle cells in culture do not express LDL receptors. Thus, pigeon macrophages have receptors for the uptake of abnormal lipoproteins that could play a role in the development of macrophage-derived foam cells that are prevalent in the early stages of atherosclerosis in this species. No quantitative or qualitative differences in these receptors, however, were identified that could account for the differences in atherosclerosis susceptibility between the WC and SR breeds.

Cholesteryl ester cycle in cultured hepatoma cells

The existence of a cholesteryl ester cycle in cultured Fu5AH hepatoma cells was documented and factors affecting the rate of turnover of the cholesteryl ester cycle in this cell line were explored. The influence of the physical state of the lipid inclusion in which the cholesteryl esters are stored could be addressed in this cell line because these cells can be induced to store cholesteryl esters in anisotropic (liquid-crystalline) cytoplasmic inclusions by exposure to free cholesterol-rich phospholipid dispersions or in isotropic (liquid) inclusions by addition of oleic acid to the phospholipid dispersions. To examine the relative rates of turnover of the cholesteryl ester cycle in the cells with the two types of inclusions, the fraction of cholesteryl linolenate, a cholesteryl ester present in low amounts in these inclusions, was examined after cells were exposed to medium containing linolenate. After 12 h, cells with anisotropic inclusions contained 17.5% cholesteryl linolenate and cells with isotropic inclusions contained 29.8% cholesteryl linolenate, suggesting an approximately 2-fold difference in turnover of the cholesteryl ester pool. To determine whether this difference was due to a differential rate of cholesteryl ester hydrolysis, the acyl CoA: cholesterol acyl transferase arm of the cholesteryl ester cycle was blocked using a specific inhibitor, Sandoz 58-035. In the presence of this compound, cholesteryl ester was hydrolysed twice as fast in cells with isotropic inclusions as compared to that in cells with anisotropic inclusions. The difference in rate of turnover of the cholesteryl ester cycle was shown to be related to the rate of hydrolysis of cholesteryl ester which, in turn, is related to the physical state of the stored cholesteryl ester.

Lipid composition and physical state effects on cellular cholesteryl ester clearance

The influence of lipid composition and physical state on the rate of cholesteryl ester clearance from cytoplasmic inclusions has been investigated. Our findings demonstrate that the increased rate of clearance correlates with an increased cellular triglyceride content and a more fluid cholesteryl ester physical state. Cultured rat hepatoma cells were induced to accumulate esterified cholesterol in a smectic liquid-crystalline state by exposure to free cholesterol-rich phospholipid dispersions. Addition of cis-unsaturated fatty acids to this loading medium (either oleate, linoleate, linolenate, or eicosadienoate) resulted in a substantial increase in cellular triglyceride content (greater than 7 times non-fatty acid-treated), cellular cholesteryl esters in a liquid state, and a rate of cholesteryl ester clearance twice that of control (approximately 34% versus 17% in 12 h). In studies with oleic acid, storage of cellular cholesteryl esters in a liquid state was found to be dependent on the presence of triglycerides, and the rate at which these cells hydrolyzed cholesteryl esters was proportional to triglyceride levels. Cells exposed to either linoleic or linolenic acid hydrolyzed cholesteryl esters at the faster rate, but in contrast to findings with oleate and eicosadienoate, the storage of cholesteryl esters in a liquid state may also be a consequence of the modified fatty acyl composition of the cholesteryl esters themselves. Addition of a saturated fatty acid (palmitate) or a fatty acid with a trans-double bond (elaidate) to the cholesterol loading media had little effect on cellular triglyceride content, cholesteryl ester physical state, or the rate of cholesteryl ester clearance.

Cellular cholesteryl ester clearance. Relationship to the physical state of cholesteryl ester inclusions

The hypothesis that clearance of cellular cholesteryl ester deposits may be a function of the physical state of the stored lipid has been investigated. Cultured rat hepatoma cells were induced to store cholesteryl ester in either anisotropic inclusions by exposure to free cholesterol-rich phospholipid dispersions or isotropic inclusions by exposure to identical dispersions supplemented with oleic acid. Differential scanning calorimetry demonstrated an order/disorder transition at 43 degrees C for cholesteryl esters stored in anisotropic inclusions; the enthalpy of this transition was consistent with a smectic liquid crystalline to liquid transition. Lipids in cells with isotropic inclusions displayed no order/disorder transitions over the range 20-80 degrees C, indicating that the lipids are in a liquid state. The presence of oleic acid did not influence the mass of cholesteryl ester stored but increased the amount of stored triglyceride. Fatty acyl compositions of the cholesteryl esters were different under the two loading conditions; in particular, there was 38% cholesteryl oleate in anisotropic inclusions and 65% cholesteryl oleate in isotropic inclusions. Kinetics of cholesteryl ester clearance from cells with either anisotropic or isotropic inclusions were studied during a 12-h exposure to acceptors of free cholesterol. In both cases, cholesteryl ester clearance is essentially linear over 12 h and is directly proportional to the initial content of cholesteryl ester. However, the fraction of initial content of cholesteryl ester cleared in 12 h is 0.17 +/- 0.05 for cells with anisotropic inclusions and 0.34 +/- 0.09 for cells with isotropic inclusions. Our data demonstrate that the more rapid clearance of cholesteryl ester by cells with isotropic inclusions can be correlated with the physical state of the cholesteryl ester.

Established cell lines from rat adipose tissue that secrete lipoprotein lipase

A number of cell lines derived from the stromal-vascular fraction of rat adipose tissue have been established that represent a variety of morphologic types. Despite their differing morphology, all of these cell lines secrete lipoprotein lipase in response to heparin. Because lipoprotein lipase secretion has been attributed to the presence of preadipocytes in the stromal-vascular fraction, we examined these cell lines for adipocyte conversion. None of the cell lines converted to adipocyte morphology when held at confluency or when exposed to media supplemented with high concentrations of fatty acid or very low density lipoproteins. These cell lines therefore do not seem to be preadipocytes, despite the presence of lipoprotein lipase. Among these cell lines are several that display the "cobblestone" morphology of endothelial cells, although they lack angiotensin-converting enzyme activity, reactivity with Factor VIII antibodies, and Weibel-Palade bodies. A number of authentic endothelial cells were found to be negative for lipoprotein lipase secretion. These data suggest that the "endothelial-like" cell lines established from adipose tissue are not endothelial cells.