Possible functional interactions of apolipoprotein B-100 segments that associate with cell proteoglycans and the ApoB/E receptor

Response to retention hypothesis as a source of targets for arterial wall-directed therapies to prevent atherosclerosis: A critical review

The subendothelial retention of circulating lipoproteins on extracellular matrix proteins and proteoglycans is one of the earliest events in the development of atherosclerosis. Multiple factors, including the size, type, composition, surrounding pH, and chemical modifications to lipoproteins, influence the electrostatic interactions between relevant moieties of the apolipoproteins on lipoproteins and the glycosaminoglycans of proteoglycans. The length and chemical composition of glycosaminoglycan chains attached to proteoglycan core proteins determine the extent of initial lipoprotein binding and retention in the artery wall. The phenomena of hyperelongation of glycosaminoglycan chains is associated with initial lipid retention and later atherosclerotic plaque formation. This review includes a summary of the current literature surrounding cellular mechanisms leading to GAG chain modification and lipid retention and discusses potential therapeutic strategies to target lipoprotein:proteoglycan interactions to prevent the development and progression of atherosclerosis.

Modification of lipoprotein metabolism and function driving atherogenesis in diabetes

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease, characterized by raised blood glucose levels and impaired lipid metabolism resulting from insulin resistance and relative insulin deficiency. In diabetes, the peculiar plasma lipoprotein phenotype, consisting in higher levels of apolipoprotein B-containing lipoproteins, hypertriglyceridemia, low levels of HDL cholesterol, elevated number of small, dense LDL, and increased non-HDL cholesterol, results from an increased synthesis and impaired clearance of triglyceride rich lipoproteins. This condition accelerates the development of the atherosclerotic cardiovascular disease (ASCVD), the most common cause of death in T2DM patients. Here, we review the alteration of structure, functions, and distribution of circulating lipoproteins and the pathophysiological mechanisms that induce these modifications in T2DM. The review analyzes the influence of diabetes-associated metabolic imbalances throughout the entire process of the atherosclerotic plaque formation, from lipoprotein synthesis to potential plaque destabilization. Addressing the different pathophysiological mechanisms, we suggest improved approaches for assessing the risk of adverse cardiovascular events and clinical strategies to reduce cardiovascular risk in T2DM and cardiometabolic diseases.

Mechanisms modulating foam cell formation in the arterial intima: exploring new therapeutic opportunities in atherosclerosis

In recent years, the role of macrophages as the primary cell type contributing to foam cell formation and atheroma plaque development has been widely acknowledged. However, it has been long recognized that diffuse intimal thickening (DIM), which precedes the formation of early fatty streaks in humans, primarily consists of lipid-loaded smooth muscle cells (SMCs) and their secreted proteoglycans. Recent studies have further supported the notion that SMCs constitute the majority of foam cells in advanced atherosclerotic plaques. Given that SMCs are a major component of the vascular wall, they serve as a significant source of microvesicles and exosomes, which have the potential to regulate the physiology of other vascular cells. Notably, more than half of the foam cells present in atherosclerotic lesions are of SMC origin. In this review, we describe several mechanisms underlying the formation of intimal foam-like cells in atherosclerotic plaques. Based on these mechanisms, we discuss novel therapeutic approaches that have been developed to regulate the generation of intimal foam-like cells. These innovative strategies hold promise for improving the management of atherosclerosis in the near future.

Engineering lentivirus envelope VSV-G for liver targeted delivery of IDOL-shRNA to ameliorate hypercholesterolemia and atherosclerosis

Lentiviral vectors (LVs) have been widely used as a tool for gene therapies. However, tissue-selective transduction after systemic delivery remains a challenge. Inducible degrader of low-density lipoprotein receptor is an attractive target for treating hypercholesterolemia. Here, a liver-targeted LV, CS8-LV-shIDOL, is developed by incorporating a hepatocyte-targeted peptide derived from circumsporozoite protein (CSP) into the lentivirus envelope for liver-targeted delivery of IDOL-shRNA (short hairpin RNA) to alleviate hypercholesterolemia. Tail-vein injection of CS8-LV-shIDOL results in extremely high accumulation in liver and nearly undetectable levels in other organs in mice. In addition, it shows superior therapeutic efficacy in lowering serum low-density lipoprotein cholesterol (LDL-C) and reducing atherosclerotic lesions over unmodified LV-shIDOL in hyperlipidemic mice. Mechanically, the envelope-engineered CS8-LV-shIDOL can enter liver cells via low-density lipoprotein receptor-related protein (LRP). Thus, this study provides a novel approach for liver-targeted delivery of IDOL-shRNA to treat hypercholesterolemia by using an envelope-engineered LV, and this delivery system has great potential for liver-targeted transgene therapy.

A novel assay to measure low-density lipoproteins binding to proteoglycans

BACKGROUND

The binding of low-density lipoprotein (LDL) to proteoglycans (PGs) in the extracellular matrix (ECM) of the arterial intima is a key initial step in the development of atherosclerosis. Although many techniques have been developed to assess this binding, most of the methods are labor-intensive and technically challenging to standardize across research laboratories. Thus, sensitive, and reproducible assay to detect LDL binding to PGs is needed to screen clinical populations for atherosclerosis risk.

OBJECTIVES

The aim of this study was to develop a quantitative, and reproducible assay to evaluate the affinity of LDL towards PGs and to replicate previously published results on LDL-PG binding.

METHODS

Immunofluorescence microscopy was performed to visualize the binding of LDL to PGs using mouse vascular smooth muscle (MOVAS) cells. An in-cell ELISA (ICE) was also developed and optimized to quantitatively measure LDL-PG binding using fixed MOVAS cells cultured in a 96-well format.

RESULTS

We used the ICE assay to show that, despite equal APOB concentrations, LDL isolated from adults with cardiovascular disease bound to PG to a greater extent than LDL isolated from adults without cardiovascular disease (p<0.05).

CONCLUSION

We have developed an LDL-PG binding assay that is capable of detecting differences in PG binding affinities despite equal APOB concentrations. Future work will focus on candidate apolipoproteins that enhance or diminish this interaction.

Drug repurposing for the treatment of COVID-19: Targeting nafamostat to the lungs by a liposomal delivery system

Despite tremendous global efforts since the beginning of the COVID-19 pandemic, still only a limited number of prophylactic and therapeutic options are available. Although vaccination is the most effective measure in preventing morbidity and mortality, there is a need for safe and effective post-infection treatment medication. In this study, we explored a pipeline of 21 potential candidates, examined in the Calu-3 cell line for their antiviral efficacy, for drug repurposing. Ralimetinib and nafamostat, clinically used drugs, have emerged as attractive candidates. Due to the inherent limitations of the selected drugs, we formulated targeted liposomes suitable for both systemic and intranasal administration. Non-targeted and targeted nafamostat liposomes (LipNaf) decorated with an Apolipoprotein B peptide (ApoB-P) as a specific lung-targeting ligand were successfully developed. The developed liposomal formulations of nafamostat were found to possess favorable physicochemical properties including nano size (119-147 nm), long-term stability of the normally rapidly degrading compound in aqueous solution, negligible leakage from the liposomes upon storage, and a neutral surface charge with low polydispersity index (PDI). Both nafamostat and ralimetinib liposomes showed good cellular uptake and lack of cytotoxicity, and non-targeted LipNaf demonstrated enhanced accumulation in the lungs following intranasal (IN) administration in non-infected mice. LipNaf retained its anti-SARS-CoV 2 activity in Calu 3 cells with only a modest decrease, exhibiting complete inhibition at concentrations >100 nM. IN, but not intraperitoneal (IP) treatment with targeted LipNaf resulted in a trend to reduced viral load in the lungs of K18-hACE2 mice compared to targeted empty Lip. Nevertheless, upon removal of outlier data, a statistically significant 1.9-fold reduction in viral load was achieved. This observation further highlights the importance of a targeted delivery into the respiratory tract. In summary, we were able to demonstrate a proof-of-concept of drug repurposing by liposomal formulations with anti-SARS-CoV-2 activity. The biodistribution and bioactivity studies with LipNaf suggest an IN or inhalation route of administration for optimal therapeutic efficacy.

Immunization using ApoB-100 peptide-linked nanoparticles reduces atherosclerosis

Active immunization with the apolipoprotein B-100 (ApoB-100) peptide P210 reduces experimental atherosclerosis. To advance this immunization strategy to future clinical testing, we explored the possibility of delivering P210 as an antigen using nanoparticles, given this approach has been used clinically. We first characterized the responses of T cells to P210 using PBMCs from patients with atherosclerotic cardiovascular disease (ASCVD). We then investigated the use of P210 in self-assembling peptide amphiphile micelles (P210-PAMs) as a vaccine formulation to reduce atherosclerosis in B6.129P2-Apoe^tm1Unc/J (ApoE^–/–) mice and P210’s potential mechanisms of action. We also generated and characterized a humanized mouse model with chimeric HLA-A*02:01/Kb in ApoE^–/– background to test the efficacy of P210-PAM immunization as a bridge to future clinical testing. P210 provoked T cell activation and memory response in PBMCs of patients with ASCVD. Dendritic cell uptake of P210-PAM and its costaining with MHC-I molecules supported its use as a vaccine formulation. In ApoE^–/– mice, immunization with P210-PAMs dampened P210-specific CD4⁺ T cell proliferative response and CD8⁺ T cell cytolytic response, modulated macrophage phenotype, and significantly reduced aortic atherosclerosis. Potential clinical relevance of P210-PAM immunization was demonstrated by reduced atherosclerosis in the humanized ApoE^–/– mouse model. Our data support experimental and translational use of P210-PAM as a potential vaccine candidate against human ASCVD.

Apolipoprotein B and Cardiovascular Disease: Biomarker and Potential Therapeutic Target

Apolipoprotein (apo) B, the critical structural protein of the atherogenic lipoproteins, has two major isoforms: apoB48 and apoB100. ApoB48 is found in chylomicrons and chylomicron remnants with one apoB48 molecule per chylomicron particle. Similarly, a single apoB100 molecule is contained per particle of very-low-density lipoprotein (VLDL), intermediate density lipoprotein, LDL and lipoprotein(a). This unique one apoB per particle ratio makes plasma apoB concentration a direct measure of the number of circulating atherogenic lipoproteins. ApoB levels indicate the atherogenic particle concentration independent of the particle cholesterol content, which is variable. While LDL, the major cholesterol-carrying serum lipoprotein, is the primary therapeutic target for management and prevention of atherosclerotic cardiovascular disease, there is strong evidence that apoB is a more accurate indicator of cardiovascular risk than either total cholesterol or LDL cholesterol. This review examines multiple aspects of apoB structure and function, with a focus on the controversy over use of apoB as a therapeutic target in clinical practice. Ongoing coronary artery disease residual risk, despite lipid-lowering treatment, has left patients and clinicians with unsatisfactory options for monitoring cardiovascular health. At the present time, the substitution of apoB for LDL-C in cardiovascular disease prevention guidelines has been deemed unjustified, but discussions continue.

Vasculoprotective properties of plasma lipoproteins from brown bears (Ursus arctos)

Plasma cholesterol and triglyceride (TG) levels are twice as high in hibernating brown bears (Ursus arctos) than healthy humans. Yet, bears display no signs of early stage atherosclerosis development when adult. To explore this apparent paradox, we analyzed plasma lipoproteins from the same 10 bears in winter (hibernation) and summer using size exclusion chromatography, ultracentrifugation, and electrophoresis. LDL binding to arterial proteoglycans (PGs) and plasma cholesterol efflux capacity (CEC) were also evaluated. The data collected and analyzed from bears were also compared with those from healthy humans. In bears, the cholesterol ester, unesterified cholesterol, TG, and phospholipid contents of VLDL and LDL were higher in winter than in summer. The percentage lipid composition of LDL differed between bears and humans but did not change seasonally in bears. Bear LDL was larger, richer in TGs, showed prebeta electrophoretic mobility, and had 5-10 times lower binding to arterial PGs than human LDL. Finally, plasma CEC was higher in bears than in humans, especially the HDL fraction when mediated by ABCA1. These results suggest that in brown bears the absence of early atherogenesis is likely associated with a lower affinity of LDL for arterial PGs and an elevated CEC of bear plasma.

Antigen- and Epitope-Delivering Nanoparticles Targeting Liver Induce Comparable Immunotolerance in Allergic Airway Disease and Anaphylaxis as Nanoparticle-Delivering Pharmaceuticals

The targeting of natural tolerogenic liver sinusoidal endothelial cells (LSEC) by nanoparticles (NPs), decorated with a stabilin receptor ligand, is capable of generating regulatory T-cells (Tregs), which can suppress antigen-specific immune responses, including to ovalbumin (OVA), a possible food allergen. In this regard, we have previously demonstrated that OVA-encapsulating poly(lactic-co-glycolic acid) (PLGA) nanoparticles eliminate allergic airway inflammation in OVA-sensitized mice, prophylactically and therapeutically. A competing approach is a nanocarrier platform that incorporates pharmaceutical agents interfering in mTOR (rapamycin) or NF-κB (curcumin) pathways, with the ability to induce a tolerogenic state in nontargeted antigen-presenting cells system-wide. First, we compared OVA-encapsulating, LSEC-targeting tolerogenic nanoparticles (TNPs) with nontargeted NPs incorporating curcumin and rapamycin (Rapa) in a murine eosinophilic airway inflammation model, which is Treg-sensitive. This demonstrated roughly similar tolerogenic effects on allergic airway inflammation by stabilin-targeting NP^OVAversus nontargeted NPs delivering OVA plus Rapa. Reduction in eosinophilic inflammation and TH2-mediated immune responses in the lung was accompanied by increased Foxp3⁺ Treg recruitment and TGF-β production in both platforms. As OVA incorporates IgE-binding as well as non-IgE-binding epitopes, the next experiment explored the possibility of obtaining immune tolerance by non-anaphylactic T-cell epitopes. This was accomplished by incorporating OVA^323-339 and OVA^257-264 epitopes in liver-targeting NPs to assess the prophylactic and therapeutic impact on allergic inflammation in transgenic OT-II mice. Importantly, we demonstrated that the major histocompatibility complex (MHC)-II binding (former) but not the MHC-I binding (latter) epitope interfered in allergic airway inflammation, improving TNP^OVA efficacy. The epitope-specific effect was transduced by TGF-β-producing Tregs. In the final phase of experimentation, we used an OVA-induced anaphylaxis model to demonstrate that targeted delivery of OVA and its MHC-II epitope could significantly suppress the anaphylaxis symptom score, mast cell release, and the late-phase inflammatory response. In summary, these results demonstrate comparable efficacy of LSEC-targeting versus pharmaceutical PLGA nanoparticles, as well as the ability of T-cell epitopes to achieve response outcomes similar to those of the intact allergens.

Structure and function of the endothelial surface layer: unraveling the nanoarchitecture of biological surfaces

Among the unsolved mysteries of modern biology is the nature of a lining of blood vessels called the 'endothelial surface layer' or ESL. In venous micro-vessels, it is half a micron in thickness. The ESL is 10 times thicker than the endothelial glycocalyx (eGC) at its base, has been presumed to be comprised mainly of water, yet is rigid enough to exclude red blood cells. How is this possible? Developments in physical chemistry suggest that the venous ESL is actually comprised of nanobubbles of CO2, generated from tissue metabolism, in a foam nucleated in the eGC. For arteries, the ESL is dominated by nanobubbles of O2 and N2 from inspired air. The bubbles of the foam are separated and stabilized by thin layers of serum electrolyte and proteins, and a palisade of charged polymer strands of the eGC. The ESL seems to be a respiratory organ contiguous with the flowing blood, an extension of, and a 'lung' in miniature. This interpretation may have far-reaching consequences for physiology.

Targeted siRNA Nanoparticles for Mammary Carcinoma Therapy

Non-viral, polymeric-based, siRNA nanoparticles (NPs) have been proposed as promising gene delivery systems. Encapsulating siRNA in targeted NPs could confer improved biological stability, extended half-life, enhanced permeability, effective tumor accumulation, and therapy. In this work, a peptide derived from apolipoprotein B100 (ApoB-P), the protein moiety of low-density lipoprotein, was used to target siRNA-loaded PEGylated NPs to the extracellular matrix/proteoglycans (ECM/PGs) of a mammary carcinoma tumor. siRNA against osteopontin (siOPN), a protein involved in breast cancer development and progression, was encapsulated into PEGylated poly(d,l-lactic-co-glycolic acid) (PLGA) NPs using the double emulsion solvent diffusion technique. The NPs obtained possessed desired physicochemical properties including ~200 nm size, a neutral surface charge, and high siOPN loading of ~5 µg/mg. ApoB-P-targeted NPs exhibited both enhanced binding to isolated ECM and internalization by MDA-MB-231 human mammary carcinoma cells, in comparison to non-targeted NPs. Increased accumulation of the targeted NPs was achieved in the primary mammary tumor of mice xenografted with MDA-MB-231 mammary carcinoma cells as well as in the lungs, one of the main sites affected by metastases. siOPN NPs treatment resulted in significant inhibition of tumor growth (similar bioactivity of both formulations), accompanied with significant reduction of OPN mRNA levels (~40% knockdown of mRNA levels). We demonstrated that targeted NPs possessed enhanced tumor accumulation with increased therapeutic potential in mice models of mammary carcinoma.

Plasma levels of apolipoprotein E and risk of ischemic heart disease in the general population

BACKGROUND AND AIMS

Triglyceride-rich lipoproteins are causally associated with high risk of ischemic heart disease (IHD), and apolipoprotein E (apoE) has a central role in their plasma clearance. While both quantitative and qualitative changes of apoE are established causes of rare dyslipidemia syndromes, it remains unclear whether plasma levels of apoE are associated with risk of IHD in the general population.

METHODS

We tested whether plasma levels of apoE at enrollment were associated with future risk of IHD and myocardial infarction (MI) in 91,695 individuals from the general population.

RESULTS

Multifactorially adjusted hazard ratios (HRs) for highest versus lowest apoE tertile were 1.15 (1.04-1.27) for IHD and 1.16 (1.00-1.36) for MI in men, and 0.94 (0.84-1.05) and 1.04 (0.85-1.26) in women. These associations were attenuated by adjustments for triglyceride levels. Corresponding HRs for highest versus lowest apoE tertile in ε33 carriers were 1.18 (1.03-1.36) for IHD and 1.21 (0.98-1.49) for MI in men, and 0.91 (0.78-1.06) and 0.93 (0.71-1.21) in women. Thus, the present associations were independent of APOE genotype.

CONCLUSION

These findings suggest that high plasma levels of apoE are associated with IHD in men but not in women. Triglyceride-rich lipoproteins may partly explain these associations.

Partial-filling affinity capillary electrophoresis and quartz crystal microbalance with adsorption energy distribution calculations in the study of biomolecular interactions with apolipoprotein E as interaction partner

Adsorption energy distribution (AED) calculations were successfully applied to partial-filling affinity capillary electrophoresis (PF-ACE) to facilitate more detailed studies of biomolecular interactions. PF-ACE with AED calculations was employed to study the interactions between two isoforms of apolipoprotein E (apoE) and dermatan sulfate (DS), and a quartz crystal microbalance (QCM) was used in combination with AED calculations to examine the interactions of the 15-amino-acid peptide fragment of apoE with DS. The heterogeneity of the interactions was elucidated. Microscale thermophoresis was used to validate the results. The interactions studied are of interest because, in vivo, apolipoprotein E localizes on DS-containing regions in the extracellular matrix of human vascular subendothelium. Two-site binding was demonstrated for the isoform apoE3 and DS, but only one-site binding for apoE2-DS. Comparable affinity constants were obtained for the apoE2-DS, apoE3-D3, and 15-amino-acid peptide of apoE-DS using the three techniques. The results show that combining AED calculations with modern biosensing techniques can open up another dimension in studies on the heterogeneity and affinity constants of biological molecules.

Impact of hypertension and renin-angiotensin system inhibitors in aortic stenosis

BACKGROUND

Experimental studies revealed that renin-angiotensin system (RAS) could play a crucial role in the pathophysiology of aortic stenosis (AS). The objectives of this study were to examine (i) the impact of hypertension on AS progression and clinical events and (ii) the effect of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin-receptor blockers (ARBs).

MATERIALS AND METHODS

In this observational study, we retrospectively analysed clinical and Doppler echocardiographic data prospectively collected in 338 patients with AS. Patients were separated into four groups: patients without hypertension and not treated by RAS medication (Ctrl group), patients with hypertension but not treated by RAS medication (HTN group), patients treated with ACEIs, and patients treated with ARBs. AS progression rate was assessed by the annualized increase in peak aortic jet velocity.

RESULTS

Compared with Ctrl group, patients in HTN group had faster stenosis progression (P = 0·01). Patients on ARBs had slower AS progression compared with Ctrl (trend P = 0·10) and HTN (P = 0·002) groups, whereas patients on ACEIs had similar progression rate compared with Ctrl group (P = NS) but lower compared with HTN group (P = 0·02). On multivariable analysis, compared with Ctrl group, HTN group was associated with faster AS progression rate (P = 0·002), whereas ARBs with slower progression (P = 0·0008). During a mean follow-up of 6·2 ± 2·4 years, HTN (hazard ratio [HR] = 2·45; P = 0·006) and ACEI (HR = 2·30; P = 0·01) groups were associated with a significant increase in all-cause mortality compared with Ctrl group, whereas ARB group (HR: 0·89; P = 0·80) not. In multivariable analysis, HTN and ACEI groups remained associated with increased mortality.

CONCLUSIONS

Hypertension is associated with significantly faster stenosis progression and higher incidence of clinical events in patients with AS. ARBs but not ACEs were found to abolish the increased risk of mortality associated with hypertension.

A molecular dynamics approach for the association of apolipoproteinB-100 and chondroitin-6-sulfate

A force field has been previously designed for a dodecasaccharide chain of chondroitin-6-sulfate (C6S) and has proved to yield valuable data going from basic conformational properties to a more detailed H-bonding network. This force field is further used here to unravel the interaction of C6S with its pathological counterpart in low density lipoprotein (LDL) particles. In particular, well-selected peptide fragment p2 (residues 3359-3377) also identified as the principal proteoglycan binding site (PPBS) of the major protein in LDL, apolipoproteinB-100 (apoB-100), was chosen. We study here the interaction between C6S and p2. The role of arginine and lysine, positively charged amino acids of p2, in the crucial interaction of C6S with LDL is highlighted. The secondary structure of p2 is shown to affect the efficiency of the interaction, as the α-helical structure of p2 allows optimal interaction with C6S also in dynamic conditions. One point mutation in p2 appeared to affect consequently p2-C6S interaction.

Apolipoprotein B binding domains: evidence that they are cell-penetrating peptides that efficiently deliver antigenic peptide for cross-presentation of cytotoxic T cells

Low-density lipoproteins (LDLs) are a good source of cholesterol, which is important in cellular homeostasis and production of steroids. Apolipoprotein B-100 (ApoB-100), the sole protein component of LDL, is known to bind to cell surface LDL receptor (LDLR) or cell surface-bound proteoglycans and to be internalized into cells. We found that APCs, consisting of macrophages and dendritic cells, upregulate LDLR on culture in vitro without obvious stimulation. In contrast, T cell populations only upregulate LDLR on activation. Thus, we strategized that tagging immunogens to ApoB-100 might be a useful means to target Ag to APCs. We generated fusion proteins consisting of receptor binding sites in ApoB-100, coupled to OVA peptide (ApoB-OVA), as Ag delivery vehicles and demonstrated that this novel delivery method successfully cross-presented OVA peptides in eliciting CTL responses. Surprisingly, internalization of ApoB-OVA peptide occurred via cell surface proteoglycans rather than LDLRs, consistent with evidence that structural elements of ApoB-100 indicate it to have cell-penetrating peptide properties. Finally, we used this strategy to assess therapeutic vaccination in a tumor setting. OVA-expressing EL-4 tumors grew progressively in mice immunized with ApoB-100 alone but regressed in mice immunized with ApoB-OVA fusion protein, coinciding with development of OVA-specific CTLs. Thus, to our knowledge, this is the first article to describe the cell-penetrating properties of a conserved human origin cell penetrating peptide that may be harnessed as a novel vaccination strategy as well as a therapeutics delivery device.

Study of the interaction of the C-reactive protein monomer with the U937 monocyte

C-reactive protein (CRP) has two structurally distinct isoforms, the CRP pentamer and the CRP monomer. A role for the CRP monomer in atherosclerosis is emerging, but the underlying mechanisms are only beginning to be understood. Monocytes are an important contributor to atherosclerosis, and foam cell formation is the hallmark of atherogenesis. However, whether the CRP monomer can directly interact with the monocytes and modulate their responses remains unknown. Furthermore, although FcgammaRIII (CD16) has been identified as the receptor for the CRP monomer on neutrophils, its role in mediating the CRP monomer's biological effects in other cell types has been questioned. In this study, we investigated the interaction of the CRP monomer with the monocytes using the U937 monocytic cell line. The CRP monomer specifically binds to U937 cells. This binding is unique in that it is independent of FcgammaRs and insensitive to protease digestion of the cell surface proteins. Further assays revealed that the CRP monomer directly incorporates into the plasma membrane. Interestingly, the presence of the CRP monomer efficiently retards oxidized low-density lipoprotein-induced foam cell formation of PMA-differentiated U937 macrophages and peripheral blood monocytic cell-derived macrophages. These findings provide additional evidence for the notion that the CRP monomer is an active CRP isoform that plays a role in atherogenesis via the direct modulation of the behavior of the monocytes.

Mapping oxidations of apolipoprotein B-100 in human low-density lipoprotein by liquid chromatography-tandem mass spectrometry

Human low-density lipoprotein (LDL) is a major cholesterol carrier in blood. Elevated concentration of low-density lipoprotein, especially when oxidized, is a risk factor for atherosclerosis and other cardiac inflammatory diseases. Past research has connected free radical initiated oxidations of LDL with the formation of atherosclerotic lesions and plaque in the arterial wall. The role of LDL protein in the associated diseases is still poorly understood, partially due to a lack of structural information. In this study, LDL was oxidized by hydroxyl radical. The oxidized protein was then delipidated and subjected to trypsin digestion. Peptides derived from trypsin digestion were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Identification of modified peptide sequences was achieved by a database search against apo B-100 protein sequences using the SEQUEST algorithm. At different hydroxyl radical concentrations, oxidation products of tyrosine, tryptophan, phenylalanine, proline, and lysine were identified. Oxidized amino acid residues are likely located on the exterior of the LDL particle in contact with the aqueous environment or directly bound to the free radical permeable lipid layer. These modifications provided insight for understanding the native conformation of apo B-100 in LDL particles. The presence of some natural variants at the protein level was also confirmed in our study.

Therapeutic approaches using host defence peptides to tackle herpes virus infections

One of the most common viral infections in humans is caused by herpes simplex virus (HSV). It can easily be treated with nucleoside analogues (e.g., acyclovir), but resistant strains are on the rise. Naturally occurring antimicrobial peptides have been demonstrated to possess antiviral activity against HSV. New evidence has also indicated that these host defence peptides are able to selectively stimulate the innate immune system to fight of infections. This review will focus on the anti-HSV activity of such peptides (both natural and synthetic), describe their mode of action and their clinical potential.

In vivo selection and validation of liver-specific ligands using a new T7 phage peptide display system

In vivo phage display is a powerful source of new peptide ligands for specific organ targeting by drugs and gene therapy vectors. Since the introduction of this methodology a decade ago, a number of peptides that preferentially react with organ-specific endothelium and parenchymal markers have been selected. One organ that has been conspicuously missing from these selection studies is the liver, which possesses a multitude of acquired and hereditary disorders and represents a highly important therapeutic target. Herein, we set out to fill this gap by introducing a novel peptide display system containing cloned sequences in the tail fiber protein (p17) of phage T7. The p17 display effectively avoids the innate immune system and is well suited both for selection of new liver-specific ligands and for validation of protein sequences that have been implicated in liver targeting by the use of conventional biochemical methods.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

The effect of heparin on structural and functional properties of low density lipoproteins

Heparin binding to human low density lipoproteins (LDL) and the effect of heparin on the ability of LDL to bind to the LDL receptor has been investigated. Emphasis has been made on the physiological conditions of temperature, pH and the ionic strength. Intrinsic fluorescence spectroscopy of LDL has been applied to follow heparin binding. Fluorescence anisotropy has been measured to describe the changes in apoB and dansyl-heparin dynamics upon binding. Eu3+-labeled LDL binding to the intact LDL receptor has been monitored by time-resolved fluorescence spectroscopy technique. We have found that heparin binds to LDL under the physiological conditions, probably by Van der Waals interactions and hydrogen bonding. Temperature seems to be the most important factor influencing the interaction. Furthermore, the presence of heparin inhibits LDL binding to the intact LDL receptor that might have consequences on the cholesterol metabolism in vivo.

Nanoscale Anionic Macromolecules Can Inhibit Cellular Uptake of Differentially Oxidized LDL

Nanoscale particles could be synthetically designed to potentially intervene in lipoprotein matrix retention and lipoprotein uptake in cells, processes central to atherosclerosis. We recently reported on lipoprotein interactions of nanoscale micelles self-assembled from amphiphilic scorpion-like macromolecules based on a lauryl chloride-mucic acid hydrophobic backbone and poly(ethylene glycol) shell. These micelles can be engineered to present varying levels of anionic chemistry, a key mechanism to induce differential retentivity of low-density lipoproteins (LDL) (Chnari, E.; Lari, H. B.; Tian, L.; Uhrich, K. E.; Moghe, P. V. Biomaterials 2005, 26, 3749). In this study, we examined the cellular interactions and the ability of carboxylate-terminated nanoparticles to modulate cellular uptake of differentially oxidized LDL. The nanoparticles were found to be highly biocompatible with cultured IC21 macrophages at all concentrations examined. When the nanoparticles as well as LDL were incubated with the cells over 24 h, a marked reduction in cellular uptake of LDL was observed in a nanoparticle concentration-dependent manner. Intermediate concentrations of nanoparticles (10(-6) M) elicited the most charge-specific reduction in uptake, as indicated by the difference in uptake due to anionic and uncharged nanoparticles. At these concentrations, anionic nanoparticles reduced LDL uptake for all degrees of oxidation (no oxidation, mild, high) of LDL, albeit with qualitative differences in the effects. The anionic nanoparticles were particularly effective at reducing the very high levels of uptake of the most oxidized level of LDL. Since complexation of LDL with anionic nanoparticles is reduced at higher degrees of LDL oxidation, our results suggest that anionic nanoparticles interfere in highly oxidized (hox) LDL uptake, likely by targeting cellular/receptor uptake mechanism, but control unoxidized LDL uptake by mechanisms related to direct LDL-nanoparticle complexation. Thus, anionically functionalized nanoparticles can modulate the otherwise unregulated internalization of differentially oxidized LDL.

Apolipoprotein B: a clinically important apolipoprotein which assembles atherogenic lipoproteins and promotes the development of atherosclerosis

Apolipoprotein (apo) B exists in two forms apoB100 and apoB48. ApoB100 is present on very low-density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and LDL. ApoB100 assembles VLDL particles in the liver. This process starts by the formation of a pre-VLDL, which is retained in the cell unless converted to the triglyceride-poor VLDL2. VLDL2 is secreted or converted to VLDL1 by a bulk lipidation in the Golgi apparatus. ApoB100 has a central role in the development of atherosclerosis. Two proteoglycan-binding sequences in apoB100 have been identified, which are important for retaining the lipoprotein in the intima of the artery. Retention is essential for the development of the atherosclerotic lesion.

The interaction of versican with its binding partners

Versican belongs to the family of the large aggregating chondroitin sulfate proteoglycans located primarily within the extracellular matrix (ECM). Versican, like other members of its family, has unique N- and C-terminal globular regions, each with multiple motifs. A large glycosaminoglycan-binding region lies between them. This review will begin by outlining these structures, in the context of ECM proteoglycans. The diverse binding partners afforded to versican by virtue of its modular design will then be examined. These include ECM components, such as hyaluronan, type I collagen, tenascin-R, fibulin-1, and -2, fibrillin-1, fibronectin, P- and L-selectins, and chemokines. Versican also binds to the cell surface proteins CD44, integrin beta 1, epidermal growth factor receptor, and P-selectin glycoprotein ligand-1. These multiple interactors play important roles in cell behaviour, and the roles of versican in modulating such processes are discussed.

A proteomic study of the apolipoproteins in LDL subclasses in patients with the metabolic syndrome and type 2 diabetes

The exchangeable apolipoproteins present in small, dense LDL (sdLDL) and large, buoyant LDL subclasses were evaluated with a quantitative proteomic approach in patients with the metabolic syndrome and with type 2 diabetes, both with subclinical atherosclerosis and the B LDL phenotype. The analyses included surface-enhanced laser adsorption/ionization, time-of-flight mass spectrometry, and subsequent identification by mass spectrometry or immunoblotting and were carried out in LDL subclasses isolated by ultracentrifugation in deuterium oxide gradients with near physiological salt concentrations. The sdLDLs of both types of patients were enriched in apolipoprotein C-III (apoC-III) and were depleted of apoC-I, apoA-I, and apoE compared with matched healthy controls with the A phenotype. The LDL complexes formed in serum from patients with diabetes with the arterial proteoglycan (PG) versican were also enriched in apoC-III. In addition, there was a significant correlation between the apoC-III content in sdLDL in patients and the apparent affinity of their LDLs for arterial versican. The unique distribution of exchangeable apolipoproteins in the sdLDLs of the patients studied, especially high apoC-III, coupled with the augmented affinity with arterial PGs, may contribute to the strong association of the dyslipidemia of insulin resistance with increased risk for cardiovascular disease.

Nanoscale anionic macromolecules for selective retention of low-density lipoproteins

Synthetically designed anionic nanocarriers that mimic the charge properties of glycosaminoglycans can potentially sequester low-density lipoproteins (LDL) during the treatment of atherosclerosis. In this study, we explore the LDL retentivity of 15-20 nm anionic micelles formed from amphiphilic scorpion-like macromolecules (AScMs) as building blocks. The macromolecules comprise four aliphatic chains attached to mucic acid and a linear polyethylene glycol (PEG) segment to form micellar nanocarriers with a hydrophobic core and hydrophilic corona. Dynamic light scattering and transmission electron microscopy studies indicate that the carboxylate-terminated nanocarriers (20 nm) sequester LDL (22 nm), resulting in complexes with a diameter of 60-90 nm, but neutral ethoxy-terminated nanocarriers do not retain LDL. Further, carboxylate-terminated nanocarriers consistently bound to unoxidized LDL (Relative Electrophoretic Mobility, REM=1.0) and mildly oxidized LDL (REM=1.5), but not highly oxidized LDL (REM=3.6), whereas the neutral nanocarriers displayed no preference/affinity at all, indicating that the nanocarrier-LDL binding is charge-dependent. The binding affinity of unoxidized LDL for differentially charged nanocarriers, formed from varying ratios of carboxylate- and ethoxy-terminated macromolecules, was quantified. The 100% carboxylated nanocarriers elicited the highest binding affinity (K(d)=567 nm), whereas mixed micelles elicited significantly lower levels of binding affinity. Our results highlight the promise of synthetically designed nanomaterials in lipoprotein retention, a key step in managing the escalation of atherosclerosis.

Smooth muscle cell biglycan overexpression results in increased lipoprotein retention on extracellular matrix: implications for the retention of lipoproteins in atherosclerosis

Lipoprotein retention on extracellular matrix (ECM) may play a central role in atherogenesis, and a specific extracellular matrix proteoglycan, biglycan, has been implicated in lipoprotein retention in human atherosclerosis. To test whether increased cellular biglycan expression results in increased retention of lipoproteins on ECM, rat aortic smooth muscle cells (SMCs) were transduced with a human biglycan cDNA-containing retroviral vector (LBSN) or with an empty retroviral vector (LXSN). To assess the importance of biglycan's glycosaminoglycan side chains in lipoprotein retention, ECM binding studies were also performed using RASMCs transduced with a retroviral vector encoding for a mutant, glycosaminoglycan-deficient biglycan (LBmutSN). Human biglycan mRNA and protein were confirmed in LBSN and LBmutSN RASMCs by Northern and Western blot analyses. HDL3+E binding to SMC ECM was increased significantly (as determined by 95% confidence intervals for binding curves) for LBSN as compared to either LXSN or LBmutSN cells; the increases for LBSN cell ECM were due primarily to an approximately 50% increase in binding sites (increased Bmax) versus LXSN cell ECM and of approximately 25% versus LBmutSN cell ECM. These results are consistent with the hypothesis that biglycan, through its glycosaminoglycan side chains, may mediate lipoprotein retention on atherosclerotic plaque ECM.

Influence of an asparagine to lysine mutation at amino acid 3516 of apolipoprotein B on low-density lipoprotein receptor binding

BACKGROUND

Three mutations in the apolipoprotein B (apoB) gene have previously been established as important causes of impaired receptor binding of LDL and, hence, Familial Defective Apolipoprotein B 100 (FDB). Previously, undescribed mutations were sought.

METHODS

Using denaturing gradient gel electrophoresis for mutation detection, DNA from 1852 new patients was examined.

RESULTS

A previously undiscovered mutation was found in codon 3516, located between known FDB mutations at codons 3500 and 3531. The new mutation introduces a positively charged amino acid-lysine-while other FDB mutations remove a positively charged residue, arginine. The phenotype was intriguing, LDL derived from N3516K heterozygotes allowed only poor growth of an LDL cholesterol-dependent cell line. ApoB-100-specific antibody MB47 bound to LDL from N3516K heterozygotes with increased affinity indicating a probable conformational change caused by the substitution. In contrast to these results, a competitive displacement assay in fibroblasts showed normal (or better) binding affinity to LDL receptors and using dynamic laser scattering no preferential accumulation of 3516K LDL particles in plasma was found.

CONCLUSION

Discovery of the mutation and characterisation of N3516K LDL reveals another naturally occurring apoB mutation that influences conformation of LDL apoB and its interaction with the LDL receptor.

The extracellular matrix on atherogenesis and diabetes-associated vascular disease

Atherosclerosis is remarkably increased in type 2 diabetes suggesting that mechanisms causing arterial lesion are enhanced by the metabolic disturbances of insulin resistance (IR) and diabetes. Several lines of research suggest that processes taking place in the arterial intima extracellular matrix may be part of a shared pathogenic mechanism. The intima extracellular matrix is where atherogenesis takes place. This layer contains fibrilar macromolecules like collagens, proteoglycans (PGs), hyaluronate, and extracellular multi-domain proteins. Specific interaction of lysine, arginine-rich segments of the apoB-100 lipoproteins, LDL, IDL and Lp (a), with the negatively charged glycosaminoglycans (GAGs) of PGs cause retention of the lipoproteins, one of the initiation process of atherogenesis. Such interactions cause structural modifications of the lipid and protein moieties of the lipoproteins that appear to increase their susceptibility to proteases, phospholipases and free radical-mediated processes. The association of apoB-lipoproteins, specially small and dense LDL, with intima PGs increases their uptake by macrophages and human arterial smooth muscle cells (HASMC) leading to 'foam cell' formation. In vitro, elevated levels of non-esterified fatty acids (NEFA) alter the matrix of endothelial cells basement membrane making them more permeable to macromolecules. NEFA cause changes in the expression of genes controlling the PGs composition of the PGs secreted by HASMC causing formation of a matrix with high affinity for LDL. These results lead us to speculate that an important component of the dyslipidemia of IR and type 2 diabetes, chronic high NEFA, may contribute to cellular alterations that cause changes of the arterial intima extracellular matrix. Such changes may increase the atherogenicity of the retention of apoB lipoproteins in the intima and contribute to the systemic alteration of the arterial wall frequently observed in IR and type 2 diabetes.

Glycosaminoglycan-lipoprotein interaction

Glycosaminoglycans (GAGs) bound to various proteoglycans (PGs) present in the cardiovascular system have been proposed to perform a wide range of functions. These include conferring viscoelastic properties; interacting with and modulating growth factors and enzymes; and as receptors and co-receptors in lipoprotein metabolism. Binding of apoB-100 lipoproteins, particularly low density lipoproteins (LDL), to GAGs of extracellular matrix PGs in arteries has been proposed to be an initiating event in development of atherosclerosis. This study was initiated with the aim of getting an overview of the binding patterns of different lipoprotein subclasses with individual GAG categories. We thus evaluated the interaction of lipoproteins with GAGs commonly found in the cardiovascular system using a gel mobility-shift assay developed for this purpose. The same procedure was used to measure lipoproteins binding to metabolically [(35)S]-labeled whole PGs prepared from three cell types, arterial smooth muscle cells, THP-1 macrophages and from HepG2 cells. The effect of GAG composition on PGs on lipoprotein binding was evaluated by enzymatic degradation of the carbohydrate chains. Heparan sulfate was found to bind beta very low density lipoproteins (beta-VLDL) and a chylomicron remnant model (beta-VLDL+apoE), but not LDL. Dermatan sulfate was found to bind LDL, but not beta-VLDL or the chylomicron remnant model. Chondroitin sulfate and heparin were found to bind all lipoproteins tested (LDL, beta-VLDL and beta-VLDL+apoE) although with different affinities. We can conclude that each lipoprotein subclass tested binds a specific assortment of the GAGs tested. The observations made contribute to the understanding of new and complex mechanisms by which carbohydrate and lipid metabolism may be linked.

The apolipoprotein E-dependent low density lipoprotein cholesteryl ester selective uptake pathway in murine adrenocortical cells involves chondroitin sulfate proteoglycans and an alpha 2-macroglobulin receptor

Cells acquire lipoprotein cholesterol by receptor-mediated endocytosis and selective uptake pathways. In the latter case, lipoprotein cholesteryl ester (CE) is transferred to the plasma membrane without endocytosis and degradation of the lipoprotein particle. Previous studies with Y1/E/tet/2/3 murine adrenocortical cells that were engineered to express apolipoprotein (apo) E demonstrated that apoE expression enhances low density lipoprotein (LDL) CE uptake by both selective and endocytic pathways. The present experiments test the hypothesis that apoE-dependent LDL CE selective uptake is mediated by scavenger receptor, class B, type I (SR-BI). Surprisingly, SR-BI expression was not detected in the Y1/E/tet/2/3 clone of Y1 adrenocortical cells, indicating the presence of a distinct apoE-dependent pathway for LDL CE selective uptake. ApoE-dependent LDL CE selective uptake in Y1/E/tet/2/3 cells was inhibited by receptor-associated protein and by activated alpha(2)-macroglobulin (alpha(2)M), suggesting the participation of the LDL receptor-related protein/alpha(2)M receptor. Reagents that inhibited proteoglycan synthesis or removed cell surface chondroitin sulfate proteoglycan completely blocked apoE-dependent LDL CE selective uptake. None of these reagents inhibited SR-BI-mediated LDL CE selective uptake in the Y1-BS1 clone of Y1 cells in which LDL CE selective uptake is mediated by SR-BI. We conclude that LDL CE selective uptake in adrenocortical cells occurs via SR-BI-independent and SR-BI-dependent pathways. The SR-BI-independent pathway is an apoE-dependent process that involves both chondroitin sulfate proteoglycans and an alpha(2)M receptor.

Phospholipase A2 and small, dense low-density lipoprotein

High levels of small, dense LDL in plasma are associated with increased risk for cardiovascular disease. There are some biochemical characteristics that may render small, dense LDL particles more atherogenic than larger, buoyant LDL particles. First, small, dense LDL particles contain less phospholipids and unesterified cholesterol in their surface monolayer than do large, buoyant LDL particles. This difference in lipid content appears to induce changes in the conformation of apolipoprotein B-100, leading to more exposure of proteoglycan-binding regions. This may be one reason for the high-affinity binding of small, dense LDL to arterial proteoglycans. Reduction of the phospholipid content in the surface monolayer LDL by treatment with secretory phospholipase A2 (sPLA2) forms small, dense LDL with an enhanced tendency to interact with proteoglycans. Circulating levels of sPLA2-IIA appears to be an independent risk factor for coronary artery disease and a predictor of cardiovascular events. In addition, in-vivo studies support the hypothesis that sPLA2 proteins contribute to atherogenesis and its clinical consequences. These data suggest that modification of LDL by sPLA2 in the arterial tissue or in plasma may be a mechanism for the generation of atherogenic lipoprotein particles in vivo, with a high tendency to be entrapped in the arterial extracellular matrix.

Postprandial lipemia and coronary risk

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

Lipoprotein lipase enhances the binding of native and oxidized low density lipoproteins to versican and biglycan synthesized by cultured arterial smooth muscle cells

Retention of low density lipoproteins (LDL) by vascular proteoglycans and their subsequent oxidation are important in atherogenesis. Lipoprotein lipase (LPL) can bind LDL and proteoglycans, although the effect of different proteoglycans to influence the ability of LPL to act as a bridge in the formation of LDL-proteoglycan complexes is unknown. Using an electrophoretic gel mobility shift assay, [(35)S]SO(4)-labeled versican and biglycan, two extracellular proteoglycans secreted by vascular cells, bound native LDL in a saturable fashion. The addition of bovine milk LPL dose-dependently increased the binding of native LDL to both versican and biglycan, approaching saturation at 30-40 microgram/ml LPL for versican and 20 microgram/ml LPL for biglycan. LDL was oxidized by several methods, including copper, 2, 2-azo-bis(2-amidinopropane)-2HCl and hypochlorite. Extensively copper- and hypochlorite-oxidized LDL bound poorly to versican and biglycan. Proteoglycan binding to LDL was correlated inversely with the extent of LDL; however, the addition of LPL to oxidized LDL together with biglycan or versican allowed the oxidized LDL to bind the proteoglycans in an LPL dose-dependent manner. Addition of LPL had a greater relative effect on the binding of extensively oxidized LDL to proteoglycans compared with native LDL. LPL had a slightly greater effect on increasing the binding of native and oxidized LDL to biglycan than versican. Thus, LPL in the artery wall might increase the atherogenicity of oxidized LDL, since it enables its binding to vascular biglycan and versican.

Glycation of plasma low density lipoproteins increases interaction with arterial proteoglycans

The increased susceptibility to atherosclerosis of diabetic individuals, may result from diabetes-associated modification in plasma low density lipoproteins (LDL) which enhance their interaction with arterial extracellular matrix proteoglycans. Using a nonhuman primate model for human diabetes, studies were conducted to examine diabetes-induced changes in LDL. Plasma LDL were isolated from control (n = 4) and streptozotocin-induced diabetic (n = 3) cynomolgus macaques by differential ultracentrifugation. An in vitro binding assay was used to measure LDL interaction with arterial proteoglycans. Significantly more diabetic LDL bound to proteoglycans than control LDL (12.9+/-0.7 microg LDL cholesterol/microg proteoglycan versus 8.9+/-0.5 microg LDL cholesterol/microg proteoglycan (mean +/- S.E.M.), P < 0.005). Glycation of LDL, determined by fructosamine content, was significantly enhanced in diabetic versus control animals (37+/-3.1 versus 20+/-1.5 micromol/l (mean +/- S.E.M.) P < 0.005). The correlation coefficient between fructosamine content of LDL and its binding to arterial proteoglycans was 0.95. No LDL compositional variables other than glycation correlated with proteoglycan binding. Removal of the glycated portion of LDL from diabetic animals returned LDL proteoglycan binding to normal. These data demonstrate that the diabetes induced glycation of LDL increases its proteoglycan binding properties: thus, a critical mechanism in atherosclerosis, enhanced LDL interaction with arterial proteoglycans, may be accelerated by the diabetic state.

Phospholipase A(2) modification of low density lipoproteins forms small high density particles with increased affinity for proteoglycans and glycosaminoglycans

The presence of a lipoprotein profile with abundance of small, dense low density lipoproteins (LDL), low levels of high density lipoproteins (HDL), and elevated levels of triglyceride-rich very low density lipoproteins is associated with an increased risk for coronary heart disease. The atherogenicity of small, dense LDL is believed to be one of the main reasons for this association. This particle contains less phospholipids (PL) and unesterified cholesterol than large LDL, and the apoB-100 appears to occupy a more extensive area at its surface. Although there are experiments that suggest a metabolic pathway leading to the overproduction of small, dense LDL, no clear molecular model exists to explain its association with atherogenesis. A current hypothesis is that small, dense LDL, because of its higher affinity for proteoglycans, is entrapped in the intima extracellular matrix and is more susceptible to oxidative modifications than large LDL. Here we describe how a specific reduction of approximately 50% of the PL of a normal buoyant LDL by immobilized phospholipase A(2) (PLA(2)) (EC 3.1.1.4) produces smaller and denser particles without inducing significant lipoprotein aggregation (<5%). These smaller LDL particles display a higher tendency to form nonsoluble complexes with proteoglycans and glycosaminoglycans than the parent LDL. Binding parameters of LDL and glycosaminoglycans and proteoglycans produced by human arterial smooth muscle cells were measured at near to physiological conditions. The PLA(2)-modified LDL has about 2 times higher affinity for the sulfated polysaccharides than control LDL. In addition, incubation of human plasma in the presence of PLA(2) generated smaller LDL and HDL particles compared with the control plasma incubated without PLA(2). These in vitro results indicate that the reduction of surface PL characteristic of small, dense LDL subfractions, besides contributing to its small size and density, may enhance its tendency to be retained by proteoglycans.

Apolipoprotein E peptide stimulation of rat ovarian theca cell androgen synthesis is mediated by members of the low density lipoprotein receptor superfamily

Ovarian androgen production is rate limiting for follicular maturation and can induce follicular atresia. Thus, it is important to define the actions of the intraovarian agents, such as apolipoprotein (apo) E, that modulate theca cell androgen production. Theca cell androgen production is stimulated at low concentrations and inhibited at higher concentrations of native apo E. The apo E peptide, acetyl-Y(LRKLRKRLLRDADDL)(2)C or acetyl-Y(141-155)(2)C, has low density lipoprotein (LDL) receptor and LDL receptor-related protein-binding activity, and it mimics the activity of native apo E in the theca-interstitial cell system. To define the role of members of the LDL receptor superfamily in the apo E peptide-mediated responses, we found that receptor-associated protein prevented the stimulation without altering the inhibition of androstenedione production. The apo E peptide (129-162), which has no LDL receptor-binding activity, did not stimulate androstenedione production. The apo E peptide acetyl-Y(141-155)(2)C did not stimulate androstenedione production when cell surface heparan sulfate proteoglycans were degraded with heparinase. The apo E peptide acetyl-Y(141-155)(2)C bound to heparin, a property of LDL receptor ligands, and in this complex the peptide had no effect on androstenedione production. These observations support the conclusion that apo E-mediated stimulation, but not inhibition, of ovarian theca cell androstenedione production was mediated by members of the LDL receptor superfamily.

CD44, a cell surface chondroitin sulfate proteoglycan, mediates binding of interferon-gamma and some of its biological effects on human vascular smooth muscle cells

Several cytokines and growth factors act on cells after their association with the glycosaminoglycan (GAG) moiety of cell surface proteoglycans (PGs). Interferon-gamma (IFN-gamma) binds to GAG; however, the relevance of this interaction for the biological activity of IFN-gamma on human cells remains to be established. Human arterial smooth muscle cells (HASMC), the main cells synthesizing PG in the vascular wall, respond markedly to IFN-gamma. We found that treatment of HASMC with chondroitinase ABC, an enzyme that degrades chondroitin sulfate GAG, reduced IFN-gamma binding by more than 50%. This treatment increased the affinity of 125I-IFN-gamma for cells from a Kd value of about 93 nM to a Kd value of about 33 nM. However, the total binding was reduced from 9. 3 +/- 0.77 pmol/microg to 3.0 +/- 0.23 pmol/mg (n = 4). Interestingly, pretreatment with chondroitinase ABC reduced significantly the cellular response toward IFN-gamma. The interaction of IFN-gamma with chondroitin sulfate GAG was confirmed by affinity chromatography of isolated cell-associated 35S-, 3H-labeled PG on a column with immobilized IFN-gamma. The cell-associated PG that binds to IFN-gamma was a chondroitin sulfate PG (CSPG). This CSPG had a core protein of approximately 110 kDa that was recognized by anti-CD44 antibodies on Western blots. High molecular weight complexes between IFN-gamma and chondroitin 6-sulfate were observed in gel exclusion chromatography. Additions of chondroitin 6-sulfate to cultured HASMC antagonized the antiproliferative effect and expression of major histocompatibility complex II antigens induced by IFN-gamma. These results indicate that IFN-gamma binds with low affinity to the chondroitin sulfate GAG moiety of the cell surface CSPG receptor CD44. This interaction may increase the local concentration of IFN-gamma at the cell surface, thus facilitating its binding to high affinity receptors and modulating the ability of IFN-gamma to signal a cellular response.