Plasmocitoma solitario de la base craneal: Reporte de tres pacientes / Solitary cranial base plasmocytoma: Three cases report

Plasmocytomas constitute a group of malignant neoplasm arise from clonal plasmatic cells being solitary extramedular form infrequent. Here we report three patients with solitary anterior and middle cranial base plasmocytoma. The importance of these tumors in differential diagnoses of cranial base lesions and the role of endoscopic endonasal biopsy before deciding definitive clinical approach was emphasized.

Los plasmocitomas constituyen neoplasias malignas de las células plasmáticas clónales. La forma extramedular solitaria en la base craneal es infrecuente. Se reportan tres pacientes con plasmocitoma solitario de la base craneal anterior y media. Se enfatiza en la importancia de esta afección en el diagnóstico diferencial de las lesiones de base de cráneo así como la biopsia endonasal endoscópica antes de decidir el tratamiento definitivo.

The dual PPARalpha/gamma agonist tesaglitazar blocks progression of pre-existing atherosclerosis in APOE*3Leiden.CETP transgenic mice.

BACKGROUND AND PURPOSE: We have evaluated the effects of a peroxisome proliferator-activated receptor (PPAR)alpha/gamma agonist on the progression of pre-existing atherosclerotic lesions in APOE*3Leiden.cholesteryl ester transfer protein (E3L.CETP) transgenic mice. EXPERIMENTAL APPROACH: E3L.CETP mice were fed a high-cholesterol diet for 11 weeks to induce atherosclerosis, followed by a low-cholesterol diet for 4 weeks to obtain a lower plasma total cholesterol level of approximately 10 mmol.L(-1). Mice were divided into three groups, which were either killed before (baseline) or after an 8 week treatment period with low-cholesterol diet without (control) or with the PPARalpha/gamma agonist tesaglitazar (10 microg.kg(-1).day(-1)). Atherosclerosis was assessed in the aortic root. KEY RESULTS: Treatment with tesaglitazar significantly reduced plasma triglycerides, total cholesterol, CETP mass and CETP activity, and increased high-density lipoprotein-cholesterol. At baseline, substantial atherosclerosis had developed. During the 8 week low-cholesterol diet, atherosclerosis progressed in the control group with respect to lesion area and severity, whereas tesaglitazar inhibited lesion progression during this period. Tesaglitazar reduced vessel wall inflammation, as reflected by decreased monocyte adhesion and macrophage area, and modified lesions to a more stabilized phenotype, with increased smooth muscle cell content in the cap and collagen content. CONCLUSIONS AND IMPLICATIONS: Dual PPARalpha/gamma agonism with tesaglitazar markedly improved the atherogenic triad by reducing triglycerides and very low-density lipoprotein-cholesterol and increasing high-density lipoprotein-cholesterol and additionally reduced cholesterol-induced vessel wall activation. These actions resulted in complete inhibition of progression and stabilization of pre-existing atherosclerotic lesions in E3L.CETP mice.

Fatty acids modulate the effect of darglitazone on macrophage CD36 expression.

BACKGROUND: Scavenger receptor-mediated uptake of cholesterol by macrophages in the arterial wall is believed to be proatherogenic. Thiazolidinediones are peroxisome proliferator-activated receptor gamma (PPARgamma)-agonists, which are used in the treatment of type II diabetes. They reduce atherogenesis in LDL receptor deficient and ApoE knockout mice, but up-regulate CD36, which may contribute to foam cell formation. The dyslipidaemia in type II diabetes is characterized by high levels of nonesterified fatty acids. Therefore we tested the effect of fatty acids and how fatty acids and the thiazolidinedione darglitazone interact in their effect on CD36 expression in human monocytes and macrophages. MATERIALS AND METHODS: Flow cytometry and reverse transcription-polymerase chain reaction were used to study CD36 expression. Cellular lipids were analyzed with high performance liquid chromatography. RESULTS: Darglitazone increased CD36 mRNA and protein expression in human macrophage cells. In the presence of 5% human serum, darglitazone increased the accumulation of triglycerides, but did not affect cholesterol ester levels. In the presence of albumin-bound oleic or linoleic acid, darglitazone did not increase CD36 mRNA, cell-surface CD36 protein or triglyceride content. Fatty acids per se increased CD36 mRNA and protein. DISCUSSION: The increase in CD36 in macrophages suggests a role for fatty acids in the regulation of foam cell formation. The results also suggest that the potentially proatherogenic CD36 up-regulating effect of thiazolidinediones in macrophages might not be present when the cells have access to physiological levels of albumin-bound fatty acids.

Intravascular hemolysis increases atherogenicity of diet-induced hypercholesterolemia in rabbits in spite of heme oxygenase-1 gene and protein induction.

Free radical mediated oxidation of apoB lipoproteins in the arterial intima appears to contribute to atherogenicity of the entrapped particles. A plausible pathogenic mechanism for oxidation is the one induced by heme leaking from erythrocytes that is then carried into the arterial wall by its high affinity for lipoproteins. In the intima, in the presence of H(2)O(2) secreted by macrophages, heme can be a potent oxidant. To study the role of heme as a promoter of oxidative stress damage in vivo we used a model of intravascular hemolysis (IVH) caused by phenylhydrazine in rabbits with and without diet-induced moderate hypercholesterolemia (MHC). Evaluation of the antioxidant status of plasma indicated that at the end of the treatment period this was compromised by the MHC-IVH. After 10 weeks the animals with combined MHC-IVH showed more of the aorta surface covered by lesions (27%+/-8, mean (SD) than the animals with only MHC (11%+/-7), in spite of having similar plasma levels of VLDL+LDL lipoproteins. The animals with only IVH, as well as the controls, showed minimal lesions (<1%). Heme oxygenase (HO-1) expression in aorta and other tissues was markedly increased in the group with MHC-IVH and it was correlated with the extent of IVH. The data suggest that the oxidative stress associated with IVH potentiates the atherogenicity of moderate hypercholesterolemia and that in spite of a strong induction of HO-1 this is not sufficient to counteract the atherogenicity of the combined condition.

Phospholipase A(2) in vascular disease.

Secretory phospholipase A(2) (PLA(2)) can be proatherogenic both in the circulation and in the arterial wall. In blood plasma, PLA(2) can modify the circulating lipoproteins and so induce formation of small dense LDL particles, which are associated with increased risk for cardiovascular disease. In the arterial wall, PLA(2) can hydrolyze lipoproteins. The PLA(2)-modified lipoproteins bind tightly to extracellular proteoglycans, which may lead to their enhanced retention in the arterial wall. The modified lipoproteins may also aggregate and fuse, which can lead to accumulation of their lipids within the extracellular matrix. The PLA(2)-modified particles are more susceptible to further modifications by other enzymes and agents and can be taken up by macrophages, leading to accumulation of intracellular lipids. In addition, lysophospholipids and free fatty acids, the hydrolysis products of PLA(2), promote atherogenesis. Thus, these lipid mediators can be carried, either by the PLA(2)-modified lipoproteins themselves or by albumin, into the arterial cells, which then undergo functional alterations. This may, in turn, lead to specific changes in the extracellular matrix, which increase the retention and accumulation of lipoproteins within the matrix. In the present article, we discuss the possible actions of PLA(2) enzymes, especially PLA(2)-IIA, in the arterial wall during atherogenesis.

Changes in matrix proteoglycans induced by insulin and fatty acids in hepatic cells may contribute to dyslipidemia of insulin resistance.

Insulin resistance and type 2 diabetes are associated with elevated circulating levels of insulin, nonesterified fatty acids (NEFAs), and lipoprotein remnants. Extracellular matrix proteoglycan (PG) alterations are also common in macro- and microvascular complications of type 2 diabetes. In liver, extracellular heparan sulfate (HS) PGs contribute to the uptake of triglyceride-rich lipoprotein remnants. We found that HepG2 cells cultured with 10 or 50 nmol/l insulin or 300 micromol/l albumin-bound linoleic acid changed their PG secretion. The glycosaminoglycans (GAGs) of the secreted PGs from insulin-treated HepG2 cells were enriched in chondroitin sulfate (CS) PGs. In contrast, cells exposed to linoleic acid secreted PGs with decreased content of CS. Insulin caused a moderate increase in mRNA for versican (secreted CS PG), whereas linoleic acid markedly decreased mRNA for versican in HepG2 cells, as did the peroxisomal proliferator-activated receptor-alpha agonist bezafibrate. The effects of insulin or linoleic acid on syndecan 1, a cell surface HS PG, were similar to those on versican, but less pronounced. The livers of obese Zucker fa/fa rats, which are insulin-resistant and have high levels of insulin, NEFAs, and triglyceride-rich remnants, showed increased expression of CS PGs when compared with lean littermates. These changes in PG composition decreased the affinity of remnant beta-VLDL particles to PGs isolated from insulin-treated HepG2 cells and obese rat livers. The results indicated that insulin and NEFAs modulate the expression of PGs in hepatic cells. We speculate that in vivo this exchange of CS for HS may reduce the clearance of remnant beta-VLDLs and contribute to the dyslipidemia of insulin resistance.

[Why are plasmatic apoB lipoproteins atherogenic? The hypothesis of response to retention]. / Por qué son aterogénicas las lipoproteínas apoB del plasma: la hipótesis de respuesta a la retención.

The development of atherosclerotic lesions can be described as a tissular response to deposition of apoB-100 containing lipoproteins (LpApoB) in the arterial intima. These particles that circulate in blood are the low-density lipoproteins (LDL), the very low and intermediate density lipoproteins (VLDL and IDL) and the Lp(a). To initiate the tissue response is critic that LpApoB are retained in the subendothelial space. This occurs by the interaction of specific positive segments of the apoB-100 with negative glycosaminoglycan chains of the proteoglycans of the intima extracellular matrix. The inflammatory response involve macrophages and other immuno-competent cells, smooth muscle cells and endothelial cells. The direct agents that induce this reaction appear to be products of hydrolytic and oxidative modifications of the phospholipids, triglycerides and sterols of the retained LpApoB. The enzymes that cause these modifications are secreted by arterial cells stimulated by pro-inflammatory cytokines. The sequence of LpApoB retention and modification in the extracellular matrix followed by proliferation and inflammation seems to be a cyclic process that leads to the chronic progress of atherosclerotic lesions. These concepts constitute the base of a new hypothesis to explain atherosclerosis: the "response to retention hypothesis".

Elevated levels of small, low-density lipoprotein with high affinity for arterial matrix components in patients with rheumatoid arthritis: possible contribution of phospholipase A2 to this atherogenic profile.

OBJECTIVE: This work studied the presence of inflammatory and atherogenic lipoprotein markers that could explain the high incidence of cardiovascular disease (CVD) reported in rheumatoid arthritis (RA) patients. METHODS: Inflammatory markers were 1) soluble adhesion molecules (intercellular adhesion molecule [ICAM] and vascular cell adhesion molecule [VCAM]), 2) C-reactive protein (CRP), 3) fibrinogen (Fb), 4) cytokines (interferon-gamma [IFNgamma], tumor necrosis factor alpha [TNFalpha]), and 5) secretory group IIA phospholipase A2 (sPLA2-IIA). Atherogenic lipoprotein markers were 1) the size distribution of plasma lipoprotein subclasses, and 2) the binding affinity of low-density lipoprotein (LDL) to chondroitin 6-sulfate glycosaminoglycan (GAG). RESULTS: RA patients (n = 31) and matched controls (n = 28) had similar plasma concentrations of total cholesterol, triglycerides, Apo B, Apo A-I, very low-density lipoprotein, intermediate-density lipoprotein, and high-density lipoprotein (HDL). RA patients had significantly higher plasma levels of sPLA2-IIA, ICAM, CRP, Fb, TNFalpha, and IFNgamma compared with controls. RA patients also had significantly higher levels of small, dense LDL-1 (P < 0.05) and lower levels of small HDL-2 particles (P < 0.001) compared with controls. In addition, LDL from RA patients had a significantly higher binding affinity (Kd) to GAG (mean +/- SD Kd 204+/-22.4 nM Apo B) than did LDL from control subjects (Kd 312+/-36 nM Apo B) (P < 0.05). This Kd value showed a significant negative correlation with the plasma levels of LDL-1 (r = -0.566, P < or = 0.004). In RA patients, a significant positive correlation was obtained between sPLA2-IIA and CRP, ICAM, and LDL-1. HDL-2 showed a negative correlation with sPLA2-IIA. CONCLUSION: These atherogenic lipoprotein factors combined with the presence of chronic inflammation may contribute to the high CVD-related mortality in RA patients.

Pharmacological treatment of insulin resistance in obesity.

AIM: To discuss new pharmacological possibilities for acting on the lipid metabolism abnormalities relating obesity, insulin resistance and arterial disease. DATA SYNTHESIS: Obesity is frequently associated with excess caloric fat dietary intake, especially in the form of fatty acids. An increased flux of fatty acids into muscle, liver and pancreas is probably a major cause of insulin resistance and possibly of pancreatic secretory disturbances. Liver exposure to fatty acid overload may also be the main reason for the atherogenic lipoprotein profile of insulin resistance and type 2 diabetes, which is characterised by prolonged post-prandial hypertriglyceridemia, high levels of large very low-density lipoproteins (VLDL) and small, dense low-density lipoproteins (LDL), and a reduced number of apoAl-containing high-density lipoproteins (HDL). This lipoprotein profile may be the main contributor to the high prevalence of arterial disease in patients with type 2 diabetes. The treatment of type 2 diabetes and insulin resistance in obese or non-obese subjects should therefore aim at normalising fatty acid fluxes because this can be expected to enhance insulin action and ameliorate the atherogenic lipoprotein abnormalities. The discovery of peroxisome proliferator-activated receptors (PPARs) and the elucidation of their function as master controllers of the genes involved in fatty acid metabolism have facilitated the development of potent modulating substances. Promising results have been obtained with the current generation of PPAR gamma ligands, but undesirable effects have also been reported. CONCLUSIONS: New knowledge concerning the structure and function of PPAR gamma and PPAR alpha is being used to develop non-TZD modulators with combined PPAR alpha and gamma actions in animal studies. This new generation of substances may offer a more balanced spectrum of activity that may be better suited for the treatment of the insulin resistance and type 2 diabetes frequently associated with obesity.

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.

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.

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.

Development and initial evaluation of a novel method for assessing tissue-specific plasma free fatty acid utilization in vivo using (R)-2-bromopalmitate tracer.

We describe a method for assessing tissue-specific plasma free fatty acid (FFA) utilization in vivo using a non-beta-oxidizable FFA analog, [9,10-3H]-(R)-2-bromopalmitate (3H-R-BrP). Ideally 3H-R-BrP would be transported in plasma, taken up by tissues and activated by the enzyme acyl-CoA synthetase (ACS) like native FFA, but then 3H-labeled metabolites would be trapped. In vitro we found that 2-bromopalmitate and palmitate compete equivalently for the same ligand binding sites on albumin and intestinal fatty acid binding protein, and activation by ACS was stereoselective for the R-isomer. In vivo, oxidative and non-oxidative FFA metabolism was assessed in anesthetized Wistar rats by infusing, over 4 min, a mixture of 3H-R-BrP and [U-14C] palmitate (14C-palmitate). Indices of total FFA utilization (R*f) and incorporation into storage products (Rfs') were defined, based on tissue concentrations of 3H and 14C, respectively, 16 min after the start of tracer infusion. R*f, but not Rfs', was substantially increased in contracting (sciatic nerve stimulated) hindlimb muscles compared with contralateral non-contracting muscles. The contraction-induced increases in R*f were completely prevented by blockade of beta-oxidation with etomoxir. These results verify that 3H-R-BrP traces local total FFA utilization, including oxidative and non-oxidative metabolism. Separate estimates of the rates of loss of 3H activity indicated effective 3H metabolite retention in most tissues over a 16-min period, but appeared less effective in liver and heart. In conclusion, simultaneous use of 3H-R-BrP and [14C]palmitate tracers provides a new useful tool for in vivo studies of tissue-specific FFA transport, utilization and metabolic fate, especially in skeletal muscle and adipose tissue.

Proteoglycans contribution to association of Lp(a) and LDL with smooth muscle cell extracellular matrix.

Lp(a) interference with fibrinolysis could contribute to atherothrombosis. Additionally, accumulation of Lp(a) and LDLs, could lead to cholesterol deposition and foam cell formation in atherogenesis. The interactions between Lp(a) and LDL could cause their entrapment in the extracellular matrix of lesions. We found that association of Lp(a) with matrix secreted by cultured human arterial smooth muscle cells increased 2 to 3 times the subsequent specific binding of radioactive LDL. Chondroitin sulfate proteoglycans seem responsible for formation of the specific matrix-Lp(a) and matrix-LDL aggregates. The proteoglycans appeared also to participate in a cooperative increase of radioactive LDL binding to matrix pretreated with Lp(a). In the matrix preincubated with LDL, approximately 50% of the additional lipoprotein was bound by ionic interactions. In the matrix preincubated with Lp(a), 20% of the additional LDL was held by ionic bonds, and the rest was held by strong nonionic associations. Binding analysis in physiological solutions confirmed that chondroitin sulfate-rich proteoglycans from the smooth muscle cell matrix have a high affinity for Lp(a) and LDL. The results provide an explanation to the observed localization of Lp(a) and LDL in the extracellular matrix of arterial lesions and suggest a mechanism for their cooperative accumulation there.

Fatty acids modulate the composition of extracellular matrix in cultured human arterial smooth muscle cells by altering the expression of genes for proteoglycan core proteins.

In diabetes-associated microangiopathies and atherosclerosis, there are alterations of the extracellular matrix (ECM) in the intima of small and large arteries. High levels of circulating nonesterified fatty acids (NEFAs) are present in insulin resistance and type 2 diabetes. High concentrations of NEFAs might alter the basement membrane composition of endothelial cells. In arteries, smooth muscle cells (SMCs) are the major producers of proteoglycans and glycoproteins in the intima, and this is the site of lipoprotein deposition and modification, key events in atherogenesis. We found that exposure of human arterial SMCs to 100-300 micromol/albumin-bound linoleic acid lowered their proliferation rate and altered cell morphology. SMCs expressed 2-10 times more mRNA for the core proteins of the proteoglycans versican, decorin, and syndecan 4 compared with control cells. There was no change in expression of fibronectin and perlecan. The decorin glycosaminoglycan chains increased in size after exposure to linoleic acid. The ECM produced by cells grown in the presence of linoleic acid bound 125I-labeled LDL more tightly than that of control cells. Darglitazone, a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, neutralized the NEFA-mediated induction of the decorin gene. This suggests that some of the NEFA effects are mediated by PPAR-gamma. These actions of NEFAs, if present in vivo, could contribute to changes of the matrix of the arterial intima associated with micro- and macroangiopathies.

Lipid mediators that modulate the extracellular matrix structure and function in vascular cells.

Treatment with moderate levels of albumin-bound, nonesterified fatty acids (NEFA) induce important alterations of the structure and functionality of proteoglycans secreted by endothelial cells and arterial smooth muscle cells. In endothelial cell monolayers, the reduction on relative amount and sulfation of heparan sulfate proteoglycans is associated with an increased permeability to albumin. In smooth muscle cells, NEFA-albumin complex increased the expression of the genes for the core proteins of the proteoglycans syndecan, decorin and perlecan. This effect appears mediated by peroxisome proliferator-activated receptor gamma (PPARg). The matrix produced by the cells treated with NEFA-albumin had a higher affinity with low-density lipoproteins (LDLs). We speculate about the possibility that under dyslipidemias associated with increased exposure of vascular cells to NEFA, like in type 2 diabetes, similar alterations may contribute to associated macrovascular and microvascular complications.

Association of apo B lipoproteins with arterial proteoglycans: pathological significance and molecular basis.

Retention of apo B-100 lipoproteins, low density lipoprotein (LDL) and probably lipoprotein(a), Lp(a), by intima proteoglycans (PGs) appears to increase the residence time needed for their structural, hydrolytic and oxidative modifications. If the rate of LDL entry exceeds the tissue capacity to eliminate the modified products, this process may be a contributor to atherogenesis and lesion advancement. LDL binds to PGs of the intima, by association of specific positive segments of the apo B-100 with the negatively-charged glycosaminoglycans (GAGs) made of chondroitin sulfate (CS), dermatan sulfate (DS) and probably heparan sulfate (HS). Small, dense LDL has a higher affinity for CS-PGs than large buoyant particles, probably because they expose more of the segments binding the GAGs than larger LDL. PGs cause irreversible structural alterations of LDL that potentiate hydrolytic and oxidative modifications. These alterations also increase LDL uptake by macrophages and smooth muscle cells. These in vitro data suggest that part of the atherogenicity of LDL may depend on its tendency to form complexes with arterial PGs in vivo. Ex vivo results support this hypothesis. Subjects with coronary heart disease have LDL with significantly higher affinity for arterial PGs. This is also a characteristic of subjects with the atherogenic lipoprotein phenotype, with high levels of small, dense LDL. The LDL-PG affinity, however can be modified by dietary or pharmacological interventions that change the composition and size of LDL. Lesion-prone intima contain PGs with a high affinity for LDL. Increased LDL entrapment at these sites may be a key step in a cyclic atherogenic process.

Hemin binding and oxidation of lipoproteins in serum: mechanisms and effect on the interaction of LDL with human macrophages.

Most models of lipoprotein oxidation by free radicals have excluded macromolecular plasma components from the system. This limits their biological significance because oxidation of lipoproteins appears to occur in the intima in the presence of a plasma ultrafiltrate. Hemin, a product of in vivo hemoglobin degradation, binds and oxidizes purified lipoproteins. However, it is not known whether this occurs in the presence of plasma components that may sequester hemin. We found that hemin in serum diluted to protein levels of the extracellular fluid (10-30%) binds to low and high density lipoproteins (LDL, HDL) with association constants in the nmol/L range. In the presence of H2O2, hemin oxidizes both lipoproteins in diluted serum with formation of conjugated dienes, thiobarbituric acid reacting substances, and F2-isoprostanes. This appeared to be caused by the high affinity of hemin with LDL and by the Fe3+ liberated that remains associated with the particles after hemin is degraded. Spectrophotometric and fluorescence experiments and electrophoresis of porphyrins complex with LDL indicated that the heme ring is buried in the lipoprotein surface-monolayer with the carboxylic groups in contact with positive regions of the protein and the solvent. Human macrophages associated and degraded 3- to 4-times more hemin-oxidized LDL in diluted serum than native LDL. It is possible then that at sites of LDL, accumulation in the extracellular intima, hemin and H2O2 production could cause oxidation with potential atherogenic consequences for cellular lipoprotein processing. This may occur even when other macromolecules of the extracellular fluid are present.