Apolipoprotein E and lipoprotein lipase increase triglyceride-rich particle binding but decrease particle penetration in arterial wall

Inflammatory Links Between Hypertriglyceridemia and Atherogenesis

PURPOSE OF REVIEW

Recent studies indicate an association between hypertriglyceridemia (HTG) and atherosclerotic cardiovascular disease (ASCVD). The purpose of this review is to discuss the potential mechanism connecting HTG and ASCVD risk and the potential efficacy of HTG-targeting therapies in ASCVD prevention.

RECENT FINDINGS

HTG, with elevations in triglyceride-rich lipoproteins (TGRL) and their remnants, are causal ASCVD risk factors. The mechanisms whereby HTG increases ASCVD risk are not well understood but may include multiple factors. Inflammation plays a crucial role in atherosclerosis. TGRL compared to low-density lipoproteins (LDL) correlate better with inflammation. TGRL remnants can penetrate endothelium and interact with macrophages leading to foam cell formation and inflammation in arterial walls, thereby contributing to atherogenesis. In addition, circulating monocytes can take up TGRL and become lipid-laden foamy monocytes, which infiltrate the arterial wall and may also contribute to atherogenesis. Novel therapies targeting HTG or inflammation are in development and have potential of reducing residual ASCVD risk associated with HTG. Clinical and preclinical studies show a causal role of HTG in promoting ASCVD, in which inflammation plays a vital role. Novel therapies targeting HTG or inflammation have potential of reducing residual ASCVD risk.

Apolipoprotein E derived from CD11c+ cells ameliorates atherosclerosis

Atherosclerosis is studied in models with dysfunctional lipid homeostasis—predominantly the ApoE^−/− mouse. The role of antigen-presenting cells (APCs) for lipid homeostasis is not clear. Using a LacZ reporter mouse, we showed that CD11c⁺ cells were enriched in aortae of ApoE^−/− mice. Systemic long-term depletion of CD11c⁺ cells in ApoE^−/− mice resulted in significantly increased plaque formation associated with reduced serum ApoE levels. In CD11c^cre+ApoE^fl/fl and Albumin^cre+ApoE^fl/fl mice, we could show that ≈70% of ApoE is liver-derived and ≈25% originates from CD11c⁺ cells associated with significantly increased atherosclerotic plaque burden in both strains. Exposure to acLDL promoted cholesterol efflux from CD11c⁺ cells and cell-specific deletion of ApoE resulted in increased inflammation reflected by increased IL-1β serum levels. Our results determined for the first time the level of ApoE originating from CD11c⁺ cells and demonstrated that CD11c⁺ cells ameliorate atherosclerosis by the secretion of ApoE.

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CD11c⁺ cells are enriched in aortae of high cholesterol-fed ApoE^−/- mice

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Depletion of CD11c⁺ cells increases plaque size in ApoE^−/- mice

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≈ 20% of serum ApoE derives from CD11c⁺ cells

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ApoE from CD11c⁺ cells contributes to protection from atherosclerosis

Heparin binding triggers human VLDL remodeling by circulating lipoprotein lipase: Relevance to VLDL functionality in health and disease

Hydrolysis of VLDL triacylglycerol (TG) by lipoprotein lipase (LpL) is a major step in energy metabolism and VLDL-to-LDL maturation. Most functional LpL is anchored to the vascular endothelium, yet a small amount circulates on TG-rich lipoproteins. As circulating LpL has low catalytic activity, its role in VLDL remodeling is unclear. We use pre-heparin plasma and heparin-sepharose affinity chromatography to isolate VLDL fractions from normolipidemic, hypertriglyceridemic, or type-2 diabetic subjects. LpL is detected only in the heparin-bound fraction. Transient binding to heparin activates this VLDL-associated LpL, which hydrolyses TG, leading to gradual VLDL remodeling into IDL/LDL and HDL-size particles. The products and the timeframe of this remodeling closely resemble VLDL-to-LDL maturation in vivo. Importantly, the VLDL fraction that does not bind heparin is not remodeled. This relatively inert LpL-free VLDL is rich in TG and apoC-III, poor in apoE and apoC-II, shows impaired functionality as a substrate for the exogenous LpL or CETP, and likely has prolonged residence time in blood, which is expected to promote atherogenesis. This non-bound VLDL fraction increases in hypertriglyceridemia and in type-2 diabetes but decreases upon diabetes treatment that restores the glycemic control. In stark contrast, heparin binding by LDL increases in type-2 diabetes triggering pro-atherogenic LDL modifications. Therefore, the effects of heparin binding are associated negatively with atherogenesis for VLDL but positively for LDL. Collectively, the results reveal that binding to glycosaminoglycans initiates VLDL remodeling by circulating LpL, and suggest heparin binding as a marker of VLDL functionality and a readout for treatment of metabolic disorders.

Effect of phytosterols on reducing low-density lipoprotein cholesterol in dogs

Hyperlipidemia is described as an increase in serum and/or plasma levels of triglycerides, cholesterol, or both. This disturbance can be primary in some cases, or combined with other comorbidities such as endocrinopathies, liver diseases, or specific drug use. Among the various ways to control dyslipidemia are specific diets, omega-3 fatty acid supplementation, or hypolipemiant treatment. Herbal medicine has been used in the human clinical routine to reduce cholesterol circulation. With an aim to expand its application in veterinary medicine, we analyzed the use of phytosterols in dogs as a potential alternative to control hypercholesterolemia. We performed lipidogram analysis in healthy dogs to examine the possible adverse effects during the treatment. Eight Beagle dogs received orally two 650 mg capsules of phytosterols (Collestra, Aché), for 15 consecutive d, along with the 2 usual meals. All animals remained clinically stable during the trial. There were significant alterations in low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels during the trial. LDL was reduced (86.8 ± 29.89 mg/dL [D0], 74.45 ± 31.58 mg/dL [D8], and 58.91 ± 18.65 mg/dL [D15]; P = 0.0442) and HDL was elevated (83.40 ± 12.05 mg/dL [D0], 86.46 ± 13.05 mg/dL [D8], and 101.5 ± 10.52 [D15]; P = 0.0141), while total cholesterol and triglyceride concentrations remained constant and within the normal range for canine species. Thus, a 1300 mg dose of phytosterols, administrated orally and fractionated along with the 2 usual meals, was capable of reducing LDL and increasing HDL concentration in healthy nondyslipidemic dogs, which makes them candidates to be included on the list of hypolipemiant drugs for clinical use in dogs with hypercholesterolemia.

The heparan sulfate proteoglycan grip on hyperlipidemia and atherosclerosis

Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of proteins involved in lipid homeostasis and inflammation. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions in the context of cardiovascular disease. The majority of cardiovascular disease-related deaths are caused by complications of atherosclerosis, a disease that results in narrowing of the arterial lumen, thereby reducing blood flow to critical levels in vital organs, such as the heart and brain. Here, we discuss novel insights into how heparan sulfate proteoglycans modulate risk factors such as hyperlipidemia and inflammation that drive the initiation and progression of atherosclerotic plaques to their clinical critical endpoint.

The GPIHBP1-LPL complex is responsible for the margination of triglyceride-rich lipoproteins in capillaries

Triglyceride-rich lipoproteins (TRLs) undergo lipolysis by lipoprotein lipase (LPL), an enzyme that is transported to the capillary lumen by an endothelial cell protein, GPIHBP1. For LPL-mediated lipolysis to occur, TRLs must bind to the lumen of capillaries. This process is often assumed to involve heparan sulfate proteoglycans (HSPGs), but we suspected that TRL margination might instead require GPIHBP1. Indeed, TRLs marginate along the heart capillaries of wild-type but not Gpihbp1⁻/⁻ mice, as judged by fluorescence microscopy, quantitative assays with infrared-dye-labeled lipoproteins, and EM tomography. Both cell-culture and in vivo studies showed that TRL margination depends on LPL bound to GPIHBP1. Notably, the expression of LPL by endothelial cells in Gpihbp1⁻/⁻ mice did not restore defective TRL margination, implying that the binding of LPL to HSPGs is ineffective in promoting TRL margination. Our studies show that GPIHBP1-bound LPL is the main determinant of TRL margination.

Avaliação de colesterol e triglicerídeos séricos em cães saudáveis suplementados com ômega n-3

A análise da concentração sérica de colesterol e triglicerídeos foi realizada em 20 cães, sem raça definida, saudáveis, 10 machos e 10 fêmeas, previamente e após a suplementação por 30 dias com ácidos graxos poli-insaturados de cadeia longa derivados do ômega n-3 (497mg ácido docosa-hexaenoico e 780mg ácido eicosapentanoico). A concentração sérica de colesterol apresentou redução significativa após a suplementação em ambos os sexos (271,6±79,8mg/dL; 236,2±67,6mg/dL, antes e após suplementação, respectivamente). Em relação à concentração sérica de triglicerídeos, houve redução apenas nas fêmeas (57,8±12,1mg/dL; 45,2±7,8mg/dL, antes e após suplementação, respectivamente), não havendo efeito da suplementação nos machos.

n-3 fatty acids reduce arterial LDL-cholesterol delivery and arterial lipoprotein lipase levels and lipase distribution

OBJECTIVE

We previously reported that saturated fat (SAT)-enriched diets increase arterial cholesteryl ester (CE) deposition, especially from LDL-selective uptake (SU), and this was associated with increased arterial lipoprotein lipase (LpL). We now question how n-3 fatty acid rich diets influence arterial cholesterol delivery and arterial LpL levels.

METHODS AND RESULTS

C57BL/6 mice were fed chow or eucaloric high-fat diets enriched in SAT or fish oil (n-3) for 12 weeks, and then injected with double radiolabeled or fluorescent-labeled human LDL to separately trace LDL-CE and LDL-apoB uptake. SAT and n-3 diets increased plasma cholesterol levels similarly; n-3 diets lowered plasma triglyceride concentrations. SAT increased arterial LDL-SU with significantly higher CE infiltration into aortic media. In contrast, n-3 markedly reduced total LDL uptake and CE deposition and abolished SU with LDL localized only in aortic intima. Disparate patterns of CE deposition between diets were consistent with distribution of arterial LpL-SAT diets induced higher LpL levels throughout the aorta; n-3 diets decreased LpL levels and limited LpL expression to the aortic intima.

CONCLUSIONS

n-3 rich diets decrease arterial total LDL delivery and abrogate LDL-SU in parallel with changing arterial wall LpL expression and distribution.

GPIHBP1: an endothelial cell molecule important for the lipolytic processing of chylomicrons

PURPOSE OF REVIEW

To summarize recent data indicating that glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1) plays a key role in the lipolytic processing of chylomicrons.

RECENT FINDINGS

Lipoprotein lipase hydrolyses triglycerides in chylomicrons at the luminal surface of the capillaries in heart, adipose tissue, and skeletal muscle. The endothelial cell molecule that facilitates the lipolytic processing of chylomicrons has never been clearly defined. Mice lacking GPIHBP1 manifest chylomicronemia, with plasma triglyceride levels as high as 5000 mg/dl. In wild-type mice, GPIHBP1 is expressed on the luminal surface of capillaries in heart, adipose tissue, and skeletal muscle. Cells transfected with GPIHBP1 bind both chylomicrons and lipoprotein lipase avidly.

SUMMARY

The chylomicronemia in Gpihbp1-deficient mice, the fact that GPIHBP1 is located within the lumen of capillaries, and the fact that GPIHBP1 binds lipoprotein lipase and chylomicrons suggest that GPIHBP1 is a key platform for the lipolytic processing of triglyceride-rich lipoproteins.

Phospholipid Transfer Protein Augments Apoptosis in THP-1–Derived Macrophages Induced by Lipolyzed Hypertriglyceridemic Plasma

OBJECTIVE

Lipolysis of triglyceride-rich lipoproteins (TGRLPs) generates phospholipid-rich surface remnants and induces cytotoxic effects in adjacent vascular cells. We hypothesized that by integrating surface remnants into HDL, phospholipid transfer protein (PLTP) alleviates cytotoxicity.

METHODS AND RESULTS

To test this hypothesis and gain insight into cytotoxicity during the postprandial phase in vivo, we injected normo-TG and hyper-TG human volunteers after a standardized fat meal (postprandial sample) with heparin, thereby stimulating lipolysis (postprandial heparinized sample). Incubation of (primary) human macrophages and primary human endothelial cells with postprandial heparinized hyper-TG plasma induced pronounced cytotoxic effects that were dose dependent on the TG content of the sample. No such effects were seen with normo-TG and postprandial hyper-TG plasma. In vitro lipolysis of VLDL and chylomicrons indicated that both lipoprotein fractions can cause cytotoxicity. Interestingly, in experiments with THP-1-derived macrophages stably transfected with PLTP, PLTP substantially augmented both net phospholipid uptake and apoptotic cell death due to postprandial heparinized hyper-TG plasma. We observed that activation of caspase-3/7, poly-ADP-ribose polymerase, and enhanced bioactivity of acid sphingomyelinase may all contribute to this augmented apoptosis.

CONCLUSIONS

Our data show that lipolysis of TGRLPs and their remodelling by PLTP interact to disturb cellular phospholipid flux and intracellular signaling processes, ultimately leading to apoptosis in human macrophages and endothelial cells.

Apolipoprotein E3- and Nitric Oxide–Dependent Modulation of Endothelial Cell Inflammatory Responses

Objective— Although apolipoprotein E3 (apoE3) is known to be atheroprotective, its mechanisms of protection in endothelial cells remain unclear.

Methods and Results— Cultured human aortic endothelial cells were stimulated with tumor necrosis factor (TNF)-α in the presence of human recombinant apoE3 solubilized in dimyristoyl phosphatidylcholine liposomes. Using flow cytometry and real-time polymerase chain reaction, a significant increase of inflammatory cell adhesion proteins (vascular cell adhesion molecule-1 and E-Selectin), and MCP-1, interleukin-8, and intercellular adhesion molecule-1 gene expression was observed within 5 hours of TNF-α exposure, which was markedly attenuated in cells coincubated with apoE3. Treatment with apoE4 resulted in increased inflammatory gene expression relative to either TNF treatment alone or TNF + apoE3 treatment. NO synthase inhibition experiments demonstrated NO to be an active participant in the actions of both TNF and apoE. To clarify the role of NO, dose-response experiments were performed with 0.03 to 300 μmol/L DEA-NONOate. Using flow cytometry and real-time polymerase chain reaction, a modulatory role of NO in TNF-induced endothelial cell activation was observed.

Conclusions— These data suggest a role of vascular wall apoE3 to balance the intracellular redox state in injured endothelial cells via NO-dependent pathways.

Hyperhomocysteinemia increases arterial permeability and stiffness in mice

We have reported that hyperhomocysteinemia (HHcy) evoked by folate depletion increases arterial permeability and stiffness in rats and that low folate without HHcy increases arterial permeability in mice. In this study, we hypothesized that HHcy independently increases arterial permeability and stiffness in mice. C57BL/6J mice that received rodent chow and water [control (Con), n = 12] or water supplemented with 0.5% l-methionine (HHcy, n = 12) for 18 ± 3 wk had plasma homocysteine concentrations of 8 ± 1 and 41 ± 1 μM, respectively ( P < 0.05), and similar liver folate (∼12 ± 2 μg folate/g liver). Carotid arterial permeability, assessed as dextran accumulation using quantitative fluorescence microscopy, was greater in HHcy (3.95 ± 0.4 ng·min−1·cm−2) versus Con (2.87 ± 0.41 ng·min−1·cm−2) mice ( P < 0.05). Stress versus strain curves generated using an elastigraph indicated that 1) maximal stress (N/mm2), 2) physiological stiffness (low-strain Young's modulus, mN/mm), and 3) maximal stiffness (high-strain Young's modulus, N/mm) were higher ( P < 0.05) in aortas from HHcy versus Con mice. Thus, chronic HHcy increases arterial permeability and stiffness. Carotid arterial permeability also was assessed in age-matched C57BL/6J mice before and after incubation with 1) xanthine (0.4 mg/ml)/xanthine oxidase (0.2 mg/ml; X/XO) to generate superoxide anion (O2−) or 50 μM dl-homocysteine in the presence of 2) vehicle, 3) 300 μM diethylamine-NONOate (DEANO; a nitric oxide donor), or 4) 10−3M 4,5-dihydroxy-1,3-benzene disulfonic acid (tiron; a nonenzymatic intracellular O2−scavenger). Compared with preincubation values, X/XO and dl-homocysteine increased ( P < 0.05) permeability by 66 ± 11% and 123 ± 8%, respectively. dl-Homocysteine-induced increases in dextran accumulation were blunted ( P < 0.05) by simultaneous incubation with DEANO or tiron. Thus, acute HHcy increases arterial permeability by generating O2−to an extent whereby nitric oxide bioavailability is reduced.

C-terminal interactions of apolipoprotein E4 respond to the postprandial state

Increased triglyceride-rich lipoproteins (TGRLs) in the postprandial state are associated with atherosclerosis. We investigated whether the postprandial state induced structural changes at the apolipoprotein E4 (apoE4) C terminus, its principal lipid binding domain, using electron paramagnetic resonance (EPR) spectroscopy of a site-directed spin label attached to the cysteine of apoE4-W264C. Spin coupling between labels located in the C termini was followed after mixing with preprandial and postprandial human plasma samples. Our results indicate that postprandial plasma triggers a reorganization of the protein such that the dipolar broadening is diminished, indicating a reduction in C-terminal interaction. The loss of spectral broadening was directly correlated with an increase in postprandial plasma triglycerides and was reduced with delipidated plasma. The spin-labeled apoE4 displayed a lipid preference of VLDL > LDL > HDL in the preprandial and postprandial states. The apoE4 shift to VLDL during the postprandial state was accompanied by a loss in spectral broadening of the protein. These findings suggest that apoE4 associated with LDL maintains self-association via its C terminus and that this association is diminished in VLDL-associated protein. Lipolyzed TGRL reflected a depletion of the C-terminal interaction of apoE4. Addition of palmitate to VLDL gave a similar response as lipolyzed TGRL, suggesting that lipolysis products play a major role in reorganizing apoE4 during the postprandial state.

Associations of apolipoprotein E exon 4 and lipoprotein lipase S447X polymorphisms with acute ischemic stroke and myocardial infarction

BACKGROUND

Because apolipoprotein E (apoE) and lipopoprotein lipase (LPL) polymorphisms interact with each other and with other factors to affect lipid metabolism, we sought to determine their separate and combined effects in association with ischemic vascular disease.

METHODS

We performed a case-control study of 816 subjects: 246 acute ischemic stroke patients, 234 acute myocardial infarction patients, and 336 controls. APOE exon 4 and LPL S447X genotypes were determined.

RESULTS

APOE epsilon2 and epsilon4 homozygotes were increased in stroke (4.5% vs. 1.0%, p = 0.008), while in myocardial infarction the epsilon4 allele was increased (12.6% vs. 9.5%, p = 0.006) but epsilon2 was decreased (3.7% vs. 12.1%, p = 0.000006). For subjects with either APOE epsilon2 or epsilon4 alleles, LPL X alleles were increased in vascular disease (OR = 2.2, p = 0.01). LPL X alleles displayed opposite tendencies toward association with disease when subjects were divided by sex, smoking, or APOE genotype. Meta-analysis and regression analysis of previous studies supported the sex and smoking dichotomies.

CONCLUSION

This is the first report of an association of vascular disease with an interaction of APOE exon 4 and LPL S447X genotypes. Therefore, APOE genotypes and LPL S447X interactions with apoE, sex, and smoking may affect the risk of myocardial infarction and ischemic stroke.

Influence of folate on arterial permeability and stiffness in the absence or presence of hyperhomocysteinemia

OBJECTIVE

Elevated plasma total homocysteine (tHcy) is associated with risk for cardiovascular disease. A common cause of mild hyperhomocysteinemia (HHcy) is folate deficiency. We sought to determine whether folate deficiency per se increases arterial permeability (quantitative fluorescence microscopy) and stiffness (vessel elastigraph), and whether the effects of folate deficiency are more severe in the presence of mild HHcy.

METHODS AND RESULTS

Heterozygous cystathionine beta-synthase (CBS)-deficient mice (CBS(+/-)) and their wild-type littermates (CBS(+/+)) were fed chow containing either standard (Con) or relatively low amounts of folate (LF) for 18+/-3 weeks. Liver folate (microg folate/g liver) and tHcy (microM), respectively, were 12+/-1 and 8+/-1 in CBS(+/+) Con mice (n=12), and 8+/-1 and 8+/-1 in CBS(+/+) LF animals (n=5). Carotid arterial permeability was &38% greater (P<0.05) in CBS(+/+) LF versus Con mice, but vascular stiffening was unaltered. Liver folate and tHcy, respectively, were 13+/-1 and 11+/-1 in CBS(+/-) Con mice (n=16), and 8+/-1 and 16+/-3 in CBS(+/-) LF animals (n=6). Carotid arterial dextran accumulation was &31% greater, and maximal strain in aortae was &20% lower (both P<0.05) in CBS(+/-) LF versus Con mice.

CONCLUSIONS

Taken together, low folate (P<0.05) combined with mild HHcy (P<0.05) in CBS(+/-) mice produced more arterial dysfunction compared with low folate alone (ie, CBS(+/+) mice). These findings may be particularly relevant to elderly individuals because tHcy and deficiencies of folate metabolism increase with age.

Differential uptake of subfractions of triglyceride-rich lipoproteins by THP-1 macrophages

It is well known that raised plasma triglycerides (TG) are positively linked to the development of coronary heart disease. However, triglycerides circulate in a range of distinct lipoprotein subfractions and the relative atherogenicity of these subfractions is not clear. In this study, three fractions of triglyceride rich lipoprotein (TRL) were isolated from normolipidaemic males according to their differing Svedberg flotation (S(f)) rates: chylomicron (CM, S(f)>400), very low-density lipoprotein (VLDL)-1 (S(f) 60-400) and VLDL-2 (S(f) 20-60). These fractions were incubated with THP-1 monocyte-derived macrophages for determination of cholesterol and TG accumulation, in the presence and absence of the lipoprotein lipase (LPL) inhibitor orlistat. Expression of LDL receptor related protein (LRP) and apolipoprotein B48 receptor (apoB48R) was also examined in both differentiating monocytes, and monocyte-derived macrophages, incubated with TRL. VLDL-1 caused a significantly greater accumulation of TG within macrophages compared to VLDL-2. Binding studies also tended to show a greater preference for VLDL-1. No change in expression of LRP or apoB48R was observed in fully differentiated macrophages incubated with VLDL-1, VLDL-2 or CM, although a greater expression of LRP mRNA was observed in differentiating monocytes exposed to VLDL-1, compared to those incubated with CM or VLDL-2. TG loading in response to all three TRL fractions was blocked by orlistat, suggesting that it is likely that the major pathway for uptake of TG was hydrolysis by LPL. Calculations suggested that direct uptake of particles accounts for between 12 and 25% of total TAG uptake. In conclusion, THP monocyte-derived macrophages demonstrate a preference for VLDL-1, both through the LPL pathway and by direct uptake of whole particles.

Effects of atorvastatin on fasting plasma and marginated apolipoproteins B48 and B100 in large, triglyceride-rich lipoproteins in familial combined hyperlipidemia

Large triglyceride (TG)-rich lipoproteins (TRLs) circulate in the blood, but they may also be present in a marginated pool, probably attached to the endothelium. It is unknown whether statins can influence this marginated pool in vivo in humans. Intravenous fat tests were performed in familial combined hyperlipidemia (FCHL) subjects before and after atorvastatin treatment and in controls to investigate whether acute increases in apoB in TRL fractions would occur, potentially reflecting the release of this TRL from a marginated pool. After a 12-h fast, a bolus injection of 10% Intralipid was given to 12 FCHL patients before and after 16-wk treatment with atorvastatin. Twelve carefully matched controls were included. For 60 min postinjection, apoB48, apoB100, and lipids were measured in TRLs. Fasting apoB100 in all TRL fractions were 2- to 3-fold higher in untreated FCHL compared with controls. ApoB48 concentrations in chylomicron fractions increased significantly within 10 min in FCHL before and after treatment, but not in controls. ApoB100 increased significantly in the chylomicron fractions in untreated FCHL and in controls, but not in FCHL after treatment. In very low density lipoprotein 1, apoB100 increased only in untreated FCHL. In very low density lipoprotein 2, apoB100 did not change in any group. These data show that increasing the number of circulating TRLs by chylomicron-like particles, results in increased plasma apoB-TRLs, probably by acute release from a marginated pool. This is a physiological process occurring in FCHL and in healthy normolipidemic subjects, but it is more pronounced in the former. Decreased marginated TRL particles in FCHL is a novel antiatherogenic property of atorvastatin.

Arterial permeability and efflux of apolipoprotein B-containing lipoproteins assessed by in situ perfusion and three-dimensional quantitative confocal microscopy

OBJECTIVES

There is accumulating evidence that an increased risk of cardiovascular disease (CVD) is not simply caused by the degree of arterial exposure to plasma lipoproteins but, in addition, is determined by the affinity of the vasculature for different lipoprotein phenotypes. In this study we compare the delivery and efflux of 2 atherogenic lipoproteins to further understand the factors that regulate cholesterol accumulation in early atherogenesis.

METHODS AND RESULTS

Lipoproteins containing apolipoprotein (apo) B100 (a low-density lipoprotein [LDL]) and apoB48 (chylomicron remnants) were isolated and differentially conjugated with fluorophores and simultaneously perfused at equivalent concentrations in situ through rabbit carotid vessels. Perfusion systems were established to quantify and differentiate between lipoprotein arterial delivery and efflux. The total average rate of delivery for LDL particles (23 nm) compared with chylomicron remnants (50 nm) was 4427 particles/min(-1) per microm3 and 452 particles/min(-1) per microm3, respectively. In contrast, the average rate of efflux was 3195 particles/min(-1) per microm3 and 163 particles/min(-1) per microm3 for LDL and chylomicron remnants, respectively.

CONCLUSIONS

Results indicate that although LDL particles have a higher rate of delivery, they efflux more readily from arterial tissue compared with the larger chylomicron remnants. Collectively, our findings highlight that lipoproteins permeate through arterial tissue differently and may be dependent on the phenotype and potential interactions with extracellular matrix components.

The effect of bupivacaine on myocardial tissue hypoxia and acidosis during ventricular fibrillation

Previously we observed that during bupivacaine-induced circulatory collapse, myocardial tissue pH declined more slowly than expected. Here we evaluated the effect of bupivacaine on myocardial acidosis induced by ventricular fibrillation. Sixteen dogs were anesthetized with 1.5% end-tidal isoflurane, the chest was opened, and a probe that measured oxygen pressure (PmO(2)), carbon dioxide pressure, pH, and temperature was inserted into myocardial tissue. After baseline measures, each dog received either 10 mg/kg bupivacaine (n = 8) or a sham saline treatment (n = 8). Three minutes later ventricular fibrillation was initiated electrically, and the rate of change in PmO(2) and pH during ventricular fibrillation was measured. Baseline physiological measures were similar in the two groups of dogs. During ventricular fibrillation there was a rapid decrease in PmO(2), and the rate of decrease was not different between sham- and bupivacaine-treated dogs. Tissue pH decreased during ventricular fibrillation, and the rate of decrease was 4 times faster in sham- compared with bupivacaine-treated dogs (P < 0.05). These results show that bupivacaine attenuated myocardial tissue acidosis during ventricular fibrillation. This potentially beneficial effect may be a result of bupivacaine's ability to inhibit myocardial lactate and carbon dioxide production. This suggests a potential clinical application of bupivacaine for myocardial preservation.

IMPLICATIONS

In this animal study pretreatment with bupivacaine attenuated the progression of myocardial acidosis during ventricular fibrillation. The dogs regained normal hemodynamic variables after lipid infusion. The findings suggest such that bupivacaine may protect the heart against ischemic acidosis.