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Reverse cholesterol transport (RCT) pathway from macrophage foam cells initiates when HDL particles cross the endothelium, enter the interstitial fluid, and induce cholesterol efflux from these cells. We injected [3H]cholesterol-loaded J774 macrophages into the dorsal skin of mice and measured the transfer of macrophage-derived [3H]cholesterol to feces [macrophage-RCT (m-RCT)]. Injection of histamine to the macrophage injection site increased locally vascular permeability, enhanced influx of intravenously administered HDL, and stimulated m-RCT from the histamine-treated site. The stimulatory effect of histamine on m-RCT was abolished by prior administration of histamine H1 receptor (H1R) antagonist pyrilamine, indicating that the histamine effect was H1R-dependent. Subcutaneous administration of two other vasoactive mediators, serotonin or bradykinin, and activation of skin mast cells to secrete histamine and other vasoactive compounds also stimulated m-RCT. None of the studied vasoactive mediators affected serum HDL levels or the cholesterol-releasing ability of J774 macrophages in culture, indicating that acceleration of m-RCT was solely due to increased availability of cholesterol acceptors in skin. We conclude that disruption of the endothelial barrier by vasoactive compounds enhances the passage of HDL into interstitial fluid and increases the rate of RCT from peripheral macrophage foam cells, which reveals a novel tissue cholesterol-regulating function of these compounds.

Atherosclerotic lesions are often hypoxic and exhibit elevated lactate concentrations and local acidification of the extracellular fluids. The acidification may be a consequence of the abundant accumulation of lipid-scavenging macrophages in the lesions. Activated macrophages have a very high energy demand and they preferentially use glycolysis for ATP synthesis even under normoxic conditions, resulting in enhanced local generation and secretion of lactate and protons. In this review, we summarize our current understanding of the effects of acidic extracellular pH on three key players in atherogenesis: macrophages, apoB-containing lipoproteins, and HDL particles. Acidic extracellular pH enhances receptor-mediated phagocytosis and antigen presentation by macrophages and, importantly, triggers the secretion of proinflammatory cytokines from macrophages through activation of the inflammasome pathway. Acidity enhances the proteolytic, lipolytic, and oxidative modifications of LDL and other apoB-containing lipoproteins, and strongly increases their affinity for proteoglycans, and may thus have major effects on their retention and the ensuing cellular responses in the arterial intima. Finally, the decrease in the expression of ABCA1at acidic pH may compromise cholesterol clearance from atherosclerotic lesions. Taken together, acidic extracellular pH amplifies the proatherogenic and proinflammatory processes involved in atherogenesis.

The mast cell is a potent immune cell known for its functions in host defense responses and diseases, such as asthma and allergies. In the past years, accumulating evidence established the contribution of the mast cell to cardiovascular diseases as well, in particular, by its effects on atherosclerotic plaque progression and destabilization. Through its release not only of mediators, such as the mast cell–specific proteases chymase and tryptase, but also of growth factors, histamine, and chemokines, activated mast cells can have detrimental effects on its immediate surroundings in the vessel wall. This results in matrix degradation, apoptosis, and enhanced recruitment of inflammatory cells, thereby actively contributing to cardiovascular diseases. In this review, we will discuss the current knowledge on mast cell function in cardiovascular diseases and speculate on potential novel therapeutic strategies to prevent acute cardiovascular syndromes via targeting of mast cells.

Human mast cells (MCs) contain TG-rich cytoplasmic lipid droplets (LDs) with high arachidonic acid (AA) content. Here, we investigated the functional role of adipose TG lipase (ATGL) in TG hydrolysis and the ensuing release of AA as substrate for eicosanoid generation by activated human primary MCs in culture. Silencing of ATGL in MCs by siRNAs induced the accumulation of neutral lipids in LDs. IgE-dependent activation of MCs triggered the secretion of the two major eicosanoids, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The immediate release of PGD2 from the activated MCs was solely dependent on cyclooxygenase (COX) 1, while during the delayed phase of lipid mediator production, the inducible COX-2 also contributed to its release. Importantly, when ATGL-silenced MCs were activated, the secretion of both PGD2 and LTC4 was significantly reduced. Interestingly, the inhibitory effect on the release of LTC4 was even more pronounced in ATGL-silenced MCs than in cytosolic phospholipase A2-silenced MCs. These data show that ATGL hydrolyzes AA-containing TGs present in human MC LDs and define ATGL as a novel regulator of the substrate availability of AA for eicosanoid generation upon MC activation.

Plasma triglyceride concentration is a biomarker for circulating triglyceride-rich lipoproteins and their metabolic remnants. Common mild-to-moderate hypertriglyceridaemia is typically multigenic, and results from the cumulative burden of common and rare variants in more than 30 genes, as quantified by genetic risk scores. Rare autosomal recessive monogenic hypertriglyceridaemia can result from large-effect mutations in six different genes. Hypertriglyceridaemia is exacerbated by non-genetic factors. On the basis of recent genetic data, we redefine the disorder into two states: severe (triglyceride concentration >10 mmol/L), which is more likely to have a monogenic cause; and mild-to-moderate (triglyceride concentration 2–10 mmol/L). Because of clustering of susceptibility alleles and secondary factors in families, biochemical screening and counselling for family members is essential, but routine genetic testing is not warranted. Treatment includes management of lifestyle and secondary factors, and pharmacotherapy. In severe hypertriglyceridaemia, intervention is indicated because of pancreatitis risk; in mild-to-moderate hypertriglyceridaemia, intervention can be indicated to prevent cardiovascular disease, dependent on triglyceride concentration, concomitant lipoprotein disturbances, and overall cardiovascular risk.

HDL particles may enter atherosclerotic lesions having an acidic intimal fluid. Therefore, we investigated whether acidic pH would affect their structural and functional properties. For this purpose, HDL2and HDL3subfractions were incubated for various periods of time at different pH values ranging from 5.5 to 7.5, after which their protein and lipid compositions, size, structure, and cholesterol efflux capacity were analyzed. Incubation of either subfraction at acidic pH induced unfolding of apolipoproteins, which was followed by release of lipid-poor apoA-I and ensuing fusion of the HDL particles. The acidic pH-modified HDL particles exhibited an enhanced ability to promote cholesterol efflux from cholesterol-laden primary human macrophages. Importantly, treatment of the acidic pH-modified HDL with the mast cell-derived protease chymase completely depleted the newly generated lipid-poor apoA-I, and prevented the acidic pH-dependent increase in cholesterol efflux. The above-found pH-dependent structural and functional changes were stronger in HDL3than in HDL2. Spontaneous acidic pH-induced remodeling of mature spherical HDL particles increases HDL-induced cholesterol efflux from macrophage foam cells, and therefore may have atheroprotective effects.

During atherogenesis, the extracellular pH of atherosclerotic lesions decreases. Here, we examined the effect of low, but physiologically plausible pH on aggregation of modified LDL, one of the key processes in atherogenesis. LDL was treated with SMase, and aggregation of the SMase-treated LDL was followed at pH 5.5–7.5. The lower the pH, the more extensive was the aggregation of identically prelipolyzed LDL particles. At pH 5.5–6.0, the aggregates were much larger (size >1 µm) than those formed at neutral pH (100–200 nm). SMase treatment was found to lead to a dramatic decrease in α-helix and concomitant increase in β-sheet structures of apoB-100. Particle aggregation was caused by interactions between newly exposed segments of apoB-100. LDL-derived lipid microemulsions lacking apoB-100 failed to form large aggregates. SMase-induced LDL aggregation could be blocked by lowering the incubation temperature to 15°C, which also inhibited the changes in the conformation of apoB-100, by proteolytic degradation of apoB-100 after SMase-treatment, and by HDL particles. Taken together, sphingomyelin hydrolysis induces exposure of protease-sensitive sites of apoB-100, whose interactions govern subsequent particle aggregation. The supersized LDL aggregates may contribute to the retention of LDL lipids in acidic areas of atherosclerosis-susceptible sites in the arterial intima.

Lipid droplets, also called lipid bodies (LB) in inflammatory cells, are important cytoplasmic organelles. However, little is known about the molecular characteristics and functions of LBs in human mast cells (MC). Here, we have analyzed the genesis and components of LBs during differentiation of human peripheral blood-derived CD34+progenitors into connective tissue-type MCs. In our serum-free culture system, the maturing MCs, derived from 18 different donors, invariably developed triacylglycerol (TG)-rich LBs. Not known heretofore, the MCs transcribe the genes for perilipins (PLIN)1-4, but not PLIN5, and PLIN2 and PLIN3 display different degrees of LB association. Upon MC activation and ensuing degranulation, the LBs were not cosecreted with the cytoplasmic secretory granules. Exogenous arachidonic acid (AA) enhanced LB genesis in Triacsin C-sensitive fashion, and it was found to be preferentially incorporated into the TGs of LBs. The large TG-associated pool of AA in LBs likely is a major precursor for eicosanoid production by MCs. In summary, we demonstrate that cultured human MCs derived from CD34+progenitors in peripheral blood provide a new tool to study regulatory mechanisms involving LB functions, with particular emphasis on AA metabolism, eicosanoid biosynthesis, and subsequent release of proinflammatory lipid mediators from these cells.

Both quantity and quality of the circulating HDL particle matter for the optimal antiatherogenic potential of HDL. This review summarizes various mechanisms capable of inducing extracellular modifications of HDL and reducing the function of HDL subclasses as cholesterol acceptors. Special emphasis is laid on the proteolytic inactivation of lipid-poor pre-migrating HDL (pre-HDL).

Entrapment of lipoprotein particles in the extracellular matrix of the arterial intima is a characteristic feature of the development of atherosclerosis, the disease behind myocardial infarction and stroke. In this study, sugars were exploited in the separation of lipoproteins by CE. Monosaccharides, disaccharides and one sugar alcohol used during ultracentrifugal isolation of lipoproteins prevented the strong and unfavorable adsorption of lipoprotein particles on the capillary wall, allowing their selective separation in uncoated fused silica capillary. The effect of ionic strength of the phosphate BGE solution on the separation at physiological pH was clarified. Asymmetrical flow field‐flow fractionation and dynamic light scattering showed that sugars affected the structure of lipoproteins by decreasing their sizes. Although in molecular dynamics simulations, only a 19 amino acid peptide of apolipoprotein B‐100 and a 15 amino acid peptide of apolipoprotein E were employed, the results also indicated a decrease in lipoprotein size, supporting the asymmetrical flow field‐flow fractionation and dynamic light scattering results.

LDL particles that enter the arterial intima become exposed to proteolytic and lipolytic modifications. The extracellular hydrolases potentially involved in LDL modification include proteolytic enzymes, such as chymase, cathepsin S, and plasmin, and phospholipolytic enzymes, such as secretory phospholipases A2(sPLA2-IIa and sPLA2-V) and secretory acid sphingomyelinase (sSMase). Here, LDL was first proteolyzed and then subjected to lipolysis, after which the effects of combined proteolysis and lipolysis on LDL fusion and on binding to human aortic proteoglycans (PG) were studied. Chymase and cathepsin S led to more extensive proteolysis and release of peptide fragments from LDL than did plasmin. sPLA2-IIa was not able to hydrolyze unmodified LDL, and even preproteolysis of LDL particles failed to enhance lipolysis by this enzyme. However, preproteolysis with chymase and cathepsin S accelerated lipolysis by sPLA2-V and sSMase, which resulted in enhanced fusion and proteoglycan binding of the preproteolyzed LDL particles. Taken together, the results revealed that proteolysis sensitizes the LDL particles to hydrolysis by sPLA2-V and sSMase. By promoting fusion and binding of LDL to human aortic proteoglycans, the combination of proteolysis and phospholipolysis of LDL particles potentially enhances extracellular accumulation of LDL-derived lipids during atherogenesis.

Secretory phospholipase A2s (sPLA2s) are considered to be important enzymes in the initiation and progression of atherosclerosis. In this review, we discuss the various mechanisms by which the direct action of the sPLA2s on LDL particles in the arterial intima may contribute to atherogenesis.

Periodontitis and Chlamydia pneumoniae infection are independent risk factors for cardiovascular diseases. The aim of this study was to investigate the effect of C. pneumoniae and Aggregatibacter actinomycetemcomitans infection on hepatic inflammation and lipid homeostasis of apolipoprotein E-deficient mice. Mice were infected with viable C. pneumoniae intranasally three times for chronic infection or once for acute infection. Viable A. actinomycetemcomitans was administered 10 times intravenously alone or in concert with C. pneumoniae. Hepatic alterations were assessed by histochemistry, lipid quantification, and fatty acid profile analysis. The RNA expression levels and the presence of pathogens in the livers and lungs were detected by quantitative real-time PCR. Both pathogens were detected in the livers of the infected animals. Chronic C. pneumoniae infection induced marked changes in hepatic lipid homeostasis. A. actinomycetemcomitans infection resulted in inflammatory cell infiltration into the liver, accompanied by elevated hepatic RNA expression levels of inflammation-related genes and higher serum amyloid A and lipopolysaccharide concentrations. Our results indicate that proatherogenic pathogens infect the liver, causing proinflammatory alterations and lipid disturbances. This infection may maintain chronic systemic inflammation attributable to atherogenesis.

Cholesteryl esters (CEs) are the water-insoluble transport and storage form of cholesterol. For both transport and storage, phospholipids and proteins embrace the CEs to form an amphipathic monolayer that surrounds the CEs. CEs are transported extracellularly in lipoproteins and are stored intracellularly as cytoplasmic lipid droplets. To clarify the molecular phenomena related to the above structures, we conducted atomistic molecular-dynamics simulations for a spherical, approximately high density lipoprotein sized lipid droplet comprised of palmitoyl-oleoyl-phosphatidylcholine (POPC) and cholesteryl oleate (CO) molecules. An additional simulation was conducted for a lamellar lipid trilayer consisting of the same lipid constituents. The density profiles showed that COs were located in the core of the spherical droplet. In trilayer simulations, CO molecules were also in the core and formed two denser strata. This is remarkable because the intra- and intermolecular behaviors of the COs were similar to previous findings from bulk COs in the fluid phase. In accordance with previous experimental studies, the solubility of COs in the POPC monolayers was found to be low. The orientation distribution of the sterol moiety with respect to the normal of the system was found to be broad, with mainly isotropic or slightly parallel orientations observed deep in the core of the lipid droplet or the trilayer, respectively. In both systems, the orientation of the sterol moiety changed to perpendicular with respect to the normal close to the phopsholipid monolayers. Of interest, within the POPC monolayers, the intramolecular conformation of the COs varied from the previously proposed horseshoe-like conformation to a more extended one. From a metabolic point of view, the observed solubilization of CEs into the phospholipid monolayers, and the conformation of CEs in the phospholipid monolayers are likely to be important regulatory factors of CE transport and hydrolysis.

Electronegative LDL [LDL(–)] is an atherogenic subfraction of plasma LDL that has increased apolipoprotein E (apoE) and apoC-III content, high density, and increased susceptibility to aggregation. These characteristics suggest that LDL(–) could bind to proteoglycans (PGs); therefore, our aim was to evaluate its affinity to PGs. Binding of LDL(–) and native LDL [LDL(+)] to human aortic PGs was determined by precipitation of LDL-glycosaminoglycan complexes, LDL incubation in PG-coated microtiter wells, and affinity chromatography on PG column. All methods showed that LDL(–) had higher binding affinity to PGs than did LDL(+). PG capacity to bind LDL(–) was increased approximately 4-fold compared with LDL(+) in precipitation and microtiter assays. Chromatography on PG column showed LDL(–) to consist of two subpopulations, one with higher and one with lower PG binding affinity than LDL(+). Unexpectedly, the lower PG affinity subpopulation had increased apoE and apoC-III content. In contrast, the high PG affinity subpopulation presented phospholipase C (PLC)-like activity and increased aggregation. These results suggest that PLC-like activity could alter LDL lipid composition, thereby promoting particle aggregation and binding to PGs. This propensity of a subpopulation of LDL(–) to bind to PGs could facilitate its retention in the extracellular matrix of arterial intima and contribute to atherosclerosis progression.

The main antiatherogenic function of HDL is to promote the efflux of cholesterol from peripheral cells and transport it to the liver for excretion in a process termed reverse cholesterol transport. The aim of this study was to evaluate the cholesterol efflux capacity in low- and high-HDL subjects by utilizing monocytes and serum from 18 low-HDL and 15 high-HDL subjects. Low and high HDL levels were defined, respectively, as HDL ≤10thand HDL ≥90thFinnish age/sex-specific percentile. Cholesterol efflux from [3H]cholesterol-oleate-acetyl-LDL-loaded monocyte-derived macrophages to standard apolipoprotein A-I (apoA-I), HDL2, and serum was measured. In addition, cholesterol efflux from acetyl-LDL-loaded human THP-1 macrophages to individual sera (0.5%) derived from the study subjects was evaluated. Cholesterol efflux to apoA-I, HDL2, and serum from macrophage foam cells derived from low- and high-HDL subjects was similar. The relative ABCA1 and ABCG1 mRNA expression levels in unloaded macrophages, as well as their protein levels in loaded macrophage foam cells, were similar in the two study groups. Cholesterol efflux from THP-1 foam cells to serum recovered from high-HDL subjects was slightly higher than that to serum from low-HDL subjects (P = 0.046). Cholesterol efflux from THP-1 macrophages to serum from study subjects correlated with serum apoB (P = 0.033), apoA-I (P = 0.004), apoA-II (P < 0.0001), and the percentage of apoA-I present in the form of preβ-HDL (P = 0.0001). Our data reveal that macrophages isolated from either low- or high-HDL subjects display similar cholesterol efflux capacity to exogenous acceptors. However, sera from low-HDL subjects have poorer cholesterol acceptor ability as compared with sera from high-HDL subjects.

The pathogenesis of aortic valve stenosis (AS) is characterized by the accumulation of LDL-derived cholesterol in the diseased valves. Since LDL particles also contain plant sterols, we investigated whether plant sterols accumulate in aortic valve lesions. Serum samples were collected from 82 patients with severe AS and from 12 control subjects. Aortic valves were obtained from a subpopulation of 21 AS patients undergoing valve surgery and from 10 controls. Serum and valvular total cholesterol and noncholesterol sterols were measured by gas-liquid chromatography. Noncholesterol sterols, including both cholesterol precursors and sterols reflecting cholesterol absorption, were detected in serum samples and aortic valves. The higher the ratios to cholesterol of the cholesterol precursors and absorption markers in serum, the higher their ratios in the stenotic aortic valves (r= 0.74, P< 0.001 for lathosterol and r= 0.88, P< 0.001 for campesterol). The valvular ratio to cholesterol of lathosterol correlated negatively with the aortic valve area (r= −0.47, P= 0.045), suggesting attenuation of cholesterol synthesis with increasing severity of AS. The higher the absorption of cholesterol, the higher the plant sterol contents in stenotic aortic valves. These findings suggest that local accumulation of plant sterols and cholesterol precursors may participate in the pathobiology of aortic valve disease.

Human atherosclerotic intima contains mast cells that secrete the neutral protease chymase into the intimal fluid, which also contains HDL-modifying proteins, such as cholesteryl ester transfer protein (CETP), in addition to abundant amounts of nascent discoidal HDL particles. Here, we studied chymase-dependent degradation of a) CETP isolated from human plasma and b) CETP-HDL complexes as well as the functional consequences of such degradations. Incubation with chymase caused a rapid cleavage of CETP, yielding a specific proteolytic pattern with a concomitant reduction in its cholesteryl ester transfer activity. These chymase-dependent effects were attenuated after CETP was complexed with HDL. This attenuation was more effective when CETP was complexed with HDL3and HDL2than with discoidal reconstituted high density lipoprotein (rHDL). Conversely, rHDL, but not spherical HDLs, was protected in such CETP complexes against functional inactivation by chymase. Thus, in contrast to the complexes of CETP with spherical HDLs, the ability of the CETP-rHDL complexes to promote cholesterol efflux from macrophage foam cells remained unchanged, despite treatment with chymase. In summary, complexation of CETP and HDL modifies their resistance to proteolytic inactivation: spherical HDLs protect CETP, and CETP protects discoidal HDL. These results suggest that in inflamed atherosclerotic intima, CETP, via its complexation with HDL, has a novel protective role in early steps of reverse cholesterol transport.

To summarize the current understanding of the pathobiology of aortic valve stenosis and portray the major advances in this field.

HDL promotes cholesterol efflux from peripheral cells via ABCA1 in the first step of reverse cholesterol transport (RCT). We investigated whether the early steps of RCT were disturbed in subjects with familial low HDL and an increased risk for early atherosclerosis. Cholesterol efflux from monocyte-derived macrophages to lipid-free apolipoprotein A-I (apoA-I; %) was measured in 22 patients with familial low HDL without Tangier disease mutations and in 21 healthy controls. In addition, we defined the different alleles of ABCA1 using single-nucleotide polymorphism haplotypes and measured ABCA1 and ABCG1 mRNA transcript levels in cholesterol-loaded macrophages. Similar ABCA1-mediated cholesterol efflux levels were observed for macrophages derived from control subjects and from low-HDL subjects. However, when efflux of cholesterol was estimated as cholesterol efflux to apoA-I (%)/relative ABCA1 mRNA expression level, cholesterol removal was significantly (P = 0.001) lower in the low-HDL group. Cholesterol-loaded macrophages from low-HDL subjects showed significantly increased levels of ABCA1 mRNA but not of ABCG1 mRNA and were more often carriers of the rare ABCA1 alleles L158 and R219K. These results suggest that defective ABCA1 function in cholesterol-loaded macrophages is one potential contributor to the impaired RCT process and the increased coronary heart disease risk in subjects with familial low HDL.

Adipophilin is an adipose differentiation–related protein expressed in lipid-containing cells. Using DNA microarray analysis, we previously found the adipophilin gene (ADFP) to be overexpressed in symptomatic carotid plaques (CP). This led us to further examine the role of adipophilin in carotid atherosclerosis relative to symptom status.

Binding of apolipoprotein B-100-containing lipoproteins (VLDL, IDL, and LDL) to proteoglycans and modifications of the lipoproteins, whether bound or unbound, are key processes in atherogenesis. The complex interplay between binding and modification has been studied at neutral pH conditions. It has been demonstrated that during atherogenesis the extracellular pH of the lesions decreases. We summarize findings suggesting that lipoprotein binding and modification are enhanced at acidic pH.

In vitro experiments have demonstrated that exogenous phospholipid transfer protein (PLTP), i.e. purified PLTP added to macrophage cultures, influences ABCA1-mediated cholesterol efflux from macrophages to HDL. To investigate whether PLTP produced by the macrophages (i.e., endogenous PLTP) is also part of this process, we used peritoneal macrophages derived from PLTP-knockout (KO) and wild-type (WT) mice. The macrophages were transformed to foam cells by cholesterol loading, and this resulted in the upregulation of ABCA1. Such macrophage foam cells from PLTP-KO mice released less cholesterol to lipid-free apolipoprotein A-I (apoA-I) and to HDL than did the corresponding WT foam cells. Also, when plasma from either WT or PLTP-KO mice was used as an acceptor, cholesterol efflux from PLTP-KO foam cells was less efficient than that from WT foam cells. After cAMP treatment, which upregulated the expression of ABCA1, cholesterol efflux from PLTP-KO foam cells to apoA-I increased markedly and reached a level similar to that observed in cAMP-treated WT foam cells, restoring the decreased cholesterol efflux associated with PLTP deficiency. These results indicate that endogenous PLTP produced by macrophages contributes to the optimal function of the ABCA1-mediated cholesterol efflux-promoting machinery in these cells. Whether macrophage PLTP acts at the plasma membrane or intracellularly or shuttles between these compartments needs further study.

A novel link between inflammation and acute coronary syndromes is emerging, in that infiltrating inflammatory cells may convert a clinically silent coronary plaque into a dangerous and potentially lethal plaque. The majority of acute atherothrombotic events now relate to erosion or rupture of such unstable plaques. Here we summarize the molecular mechanisms by which activated mast cells may contribute to plaque erosion or rupture.

In familial hypercholesterolemia, a defect in low-density lipoprotein receptors causes lifelong two- to threefold elevations in serum low-density lipoprotein-cholesterol levels. This leads to early atherosclerotic changes in infancy. Lifelong hypolipidemic treatment that can be started at a young age is thus greatly needed. Early diagnosis of familial hypercholesterolemia is important, and improved DNA tests for low-density lipoprotein receptor mutations have made it possible to carry out diagnosis at birth. A low saturated-fat, low cholesterol diet can be safely started at 7 months of age. This can be accompanied by dietary stanol esters from 2 years of age. At the age of 10, statin treatment can be safely started. In adults, more aggressive hypolipidemic treatment is required in order to reach the treatment goal for serum low-density lipoprotein-cholesterol levels less than 2.5 mmol/l. This can be achieved by using high doses of statin, or preferably by combining a statin with resin or ezetimibe (Zeita®, Merck and Shering–Plough Pharmaceuticals). Once started, treatment of familial hypercholesterolemia is lifelong.

Atherosclerosis is characterized by a strong inflammatory component. One factor contributing to inflammation in the arterial intima is the complement system. Here we summarize recent progress in the field of complement research on atherogenesis.

Cardiac mast cells participate in myocardial dysfunction, but the mechanisms are presently unknown.

Bradykinin exerts cardioprotective effects through bradykinin type-2 receptors (BK-2Rs). After acute myocardial infarction in rat, the heart adapts by increasing its number of BK-2Rs. However, in human chronic end-stage heart failure, the number of BK-2Rs is significantly decreased. Thus, the presence of a cardioprotective BK-2R signaling system may be critical in the prevention of pressure overload-induced heart failure.

Mast cell chymase, a chymotrypsin-like neutral protease, can proteolyze HDL3. Here we studied the ability of rat and human chymase to proteolyze discoidal pre beta-migrating reconstituted HDL particles (rHDLs) containing either apolipoprotein A-I (apoA-I) or apoA-II. Both chymases cleaved apoA-I in rHDL at identical sites, either at the N-terminus (Tyr18 or Phe33) or at the C-terminus (Phe225), so generating three major truncated polypeptides that remained bound to the rHDL. The cleavage sites were independent of the size of the rHDL particles, but small particles were more susceptible to degradation than bigger ones. Chymase-induced truncation of apoA-I yielded functionally compromised rHDL with reduced ability to promote cellular cholesterol efflux. In sharp contrast to apoA-I, apoA-II was resistant to degradation. However, when apoA-II was present in rHDL that also contained apoA-I, it was degraded by chymase. We conclude that chymase reduces the ability of apoA-I in discoidal rHDL particles to induce cholesterol efflux by cleaving off either its amino- or carboxy-terminal portion. This observation supports the concept that limited extracellular proteolysis of apoA-I is one pathophysiologic mechanism leading to the generation and maintenance of foam cells in atherosclerotic lesions.

C-reactive protein (CRP), an acute-phase reactant, is present in atherosclerotic human arterial intima in association with lipids. In the present work we studied interactions between CRP and LDL on microtitre wells, where either CRP or LDL was immobilized. LDL was modified by vortex-mixing, oxidation, or by lipolysis with phospholipase A2 or with sphingomyelinase or a combination of trypsin and cholesterol esterase. We found that CRP bound only to LDL modified by trypsin/cholesterol esterase or by sphingomyelinase and that this binding was Ca2+-dependent. In these two forms of modified LDL, non-esterified cholesterol was susceptible to cholesterol oxidase, indicating exposure of non-esterified cholesterol on particle surfaces and suggesting a role for non-esterified cholesterol in mediating CRP binding. Consistent with this hypothesis were the following findings: (i) increasing the amount of non-esterified cholesterol in LDL with cyclodextrin increased, and decreasing its amount decreased, the binding of CRP to LDL; (ii) modification of non-esterified cholesterol in LDL by cholesterol oxidase decreased the binding of CRP to LDL; and (iii) CRP bound to purified non-esterified cholesterol. The binding was Ca2+-dependent and could be competed out with phosphocholine. Taken together, these findings suggest that CRP can bind to modified lipoproteins, notably to the non-esterified cholesterol on their surface. These interactions may be related to the suggested role of CRP in the local inflammation present in atherosclerotic plaques.