Effects of oxidation on changes of compressibility of bovine serum albumin

The methods of ultrasound velocity and density measurements were used to study the adiabatic compressibility of bovine serum albumin (BSA) during its oxidation by the prooxidants Cu2+ and 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH). We did not find changes of compressibility of BSA in the presence of copper ions at rather high molar ratio Cu2+/BSA = 0.66 mol/mol. This can be explained by binding of the Cu2+ to the binding site of BSA and thus protecting the prooxidant action of the copper. However, AAPH-mediated oxidation of BSA resulted in an increase of its apparent specific compressibility (psik/beta0). These changes could be caused by the fragmentation of the protein.     

Specific volume and compressibility of human serum albumin-polyanion complexes

The ultrasound velocimetry, densitometry, and differential scanning calorimetry have been used to study the formation of the complexes between human serum albumin (HSA) and polyanions heparin (HEP) and/or dextran sulfate (DS). The values of the ultrasound velocity and specific volume allowed us to determine the specific adiabatic compressibility, phi(K)/beta(0), which reflects the degree of volume compressibility of the complexes. We showed that in the presence of HEP and DS the adiabatic compressibility of HSA decreases with increasing concentration of polyanions. HEP more strongly interacts with HSA than DS. pH of electrolyte in the range 4.7-8.5 weakly affects the adiabatic compressibility. Changes of compressibility of HSA can be caused by increase of the hydration due to the formation of the HSA-polyanion complexes and due to partial unfolding of HSA. The HSA-polyanion interaction resulted in decrease of phase transition temperature of the protein. This evidences about protein destabilization in the presence of polyanions.     

Changes in the contractibility of the cytochrome c globule during redox transition

Changes of the volume and compressibility of cytochrome c molecule in solution during red-ox transition were investigated using differential measurements of density and ultrasound velocity. Small changes were obtained: intrinsic compressibility of the globule increases by (2.5 +/- 1)% and intrinsic volume increases by not more than 0.2%. The results are in contradiction with the recently reported data of Eden et al. claiming that oxidation of the protein is accompanied by a large, of about 40%, increase of compressibility. The validity of our results is verified by three different methods; by comparison of independently measured absolute values of apparent volumes and compressibilities of the oxidized and reduced protein (i); by differential densimetric and ultrasound velocimetric titrations of oxidized cytochrome with ascorbate (ii) and of reduced cytochrome with ferricyanide (iii). The obtained data lead to the conclusion that oxidation-induced-changes of the root mean square amplitude for intramolecular motion of atoms of cytochrome c globule is really 50-fold less than that estimated from X-ray data.     

Age-related decrease of dehydroepiandrosterone concentrations in low density lipoproteins and its role in the susceptibility of low density lipoproteins to lipid peroxidation

The incidence of atherosclerosis and related diseases increases with age. The aging process may enhance lipoprotein modification, which leads to an increase in the susceptibility of low density lipoprotein (LDL) and high density lipoprotein (HDL) to oxidation. Dehydroepiandrosterone (DHEA), the most abundant steroid hormone in humans, has been shown to have antiatherogenic effects. This hormone also decreases dramatically with age. In the present study, we were interested in determining the presence of DHEA/DHEAS (dehydroepiandrosterone sulfate) and changes in their concentrations in HDL and LDL lipoproteins with age. Moreover, we studied the susceptibility of LDL to oxidation with age in the presence or absence of vitamin E or DHEA. We demonstrated that vitamin E is unable to restore the decreased resistance to oxidation of LDL from elderly subjects to that of LDL obtained from young subjects. Furthermore, our results provide evidence that DHEA is an integral part of LDL and HDL and disappears to almost nondetectable levels during aging. The DHEA incorporated into the LDL from elderly subjects increased LDL resistance to oxidation in a concentration-dependent manner. The increased resistance provided by DHEA was higher than that with vitamin E. DHEA seems to act either by protecting vitamin E from disappearance from LDL under oxidation or by scavenging directly the free radicals produced during the oxidative process. Our results suggests that DHEA exerts an antioxidative effect on LDL, which could have antiatherogenic consequences. Careful clinical trials of DHEA replacement should determine whether this ex vivo effect could be translated into any measurable antiatherogenic (cardioprotective) action.     

Analysis of the distribution of low density lipoprotein flotation coefficients using an analytical centrifuge equipped with absorption optics

Procedure of polydispersity determinations of low density lipoproteins (LDL) on low concentration scale (0.04%) using analytical ultracentrifuge with absorption optics was produced. No corrections for Johnston-Ogston effect and hydrostatic compressibility effect are required. Isothermal compressibility of LDL particles was estimated to be equal to 1.9 X 10(-5) Bar-1. An equation was obtained relating the flotation coefficients of LDL from different sources with solvent density and buoyant density of their particles. It was revealed that LDL particles from individual human plasma are divided into three-four subgroups having specific flotation characteristics and particular quantities of the material in these subgroups.     

Low density lipoprotein stimulation of human macrophage proteoglycan secretion

Lipoprotein trapping in arterial intima increases the risk for lipoprotein oxidation, foam cell formation, and inflammatory response in surrounding cells. Modified lipoproteins increase smooth muscle cell production of proteoglycans likely to retain lipoproteins in intimal extracellular matrix. We hypothesized that macrophage proteoglycan production is regulated in a similar manner, and characterized glycosaminoglycan side chains of secreted proteoglycans. Incubation with native low density lipoproteins (LDL) strongly stimulates total proteoglycan secretion in a time and concentration dependent manner. The main secretion product is small-sized (120 kDa) with unusually long galactosaminoglycan chains, predominantly chondroitin-6-O-sulfated. The effect appears specific for native LDL; oxidized LDL, very low density lipoproteins or phospholipid liposomes have only minor effects compared to control. These observations suggest that native LDL stimulate macrophages to secrete a chondroitin sulfate-rich proteoglycan moiety likely to have high capacity for vascular extracellular trapping of apolipoprotein B-containing lipoproteins.     

Detection of apolipoprotein B100 early conformational changes during oxidation

Conformational changes of human plasma apolipoprotein B100 (apoB) during oxidative modification of low-density lipoproteins (LDL) have been investigated. Emphasis has been put on the early stages of LDL oxidation and the modification of apoB. We have applied two different modes of LDL oxidation initiation in order to approach the problem from different perspectives. To study conformational changes of the protein and the phospholipids surface monolayer, we have applied attenuated total reflection infrared as well as fluorescence spectroscopy. We have found for the first time that conformational changes of apoB occur even in the earliest stages of oxidation process and that those are located predominantly in the beta-sheet regions. The dynamics of changes has also been described and related to different stages of oxidation. After initial increase in particle surface accessibility and mobility, by entering into the propagation phase of oxidation process, LDL surface accessibility and mobility are decreased. Finally, in the decomposition phase of LDL oxidation, as the particle faces large chemical and physical changes, surface mobility and accessibility is increased again. These observations provide new insights into the modifications of LDL particles upon oxidation.     

Detection of apolipoprotein B100 early conformational changes during oxidation

Conformational changes of human plasma apolipoprotein B100 (apoB) during oxidative modification of low-density lipoproteins (LDL) have been investigated. Emphasis has been put on the early stages of LDL oxidation and the modification of apoB. We have applied two different modes of LDL oxidation initiation in order to approach the problem from different perspectives. To study conformational changes of the protein and the phospholipids surface monolayer, we have applied attenuated total reflection infrared as well as fluorescence spectroscopy. We have found for the first time that conformational changes of apoB occur even in the earliest stages of oxidation process and that those are located predominantly in the β-sheet regions. The dynamics of changes has also been described and related to different stages of oxidation. After initial increase in particle surface accessibility and mobility, by entering into the propagation phase of oxidation process, LDL surface accessibility and mobility are decreased. Finally, in the decomposition phase of LDL oxidation, as the particle faces large chemical and physical changes, surface mobility and accessibility is increased again. These observations provide new insights into the modifications of LDL particles upon oxidation.     

Kinetic analysis of copper-induced peroxidation of HDL, autoaccelerated and tocopherol-mediated peroxidation

Comparison of the kinetic profiles of copper-induced peroxidation of HDL and LDL at different copper concentrations reveals that under all the studied experimental conditions HDL is more susceptible to oxidation than LDL. The mechanism responsible for HDL oxidation is a complex function of the copper/HDL ratio and of the tocopherol content of the HDL. At high copper concentrations, the kinetic profiles were similar to those observed for LDL oxidation, namely, relatively rapid accumulation of oxidation products, via an autoaccelerated, noninhibited mechanism, was preceded by an initial "lag phase." Under these conditions, the maximal peroxidation rate (V(max)) of HDL and LDL depended similarly on the molar ratio of bound copper/lipoprotein. Analysis of this dependency in terms of the binding characteristics of copper to lipoprotein, yielded similar dissociation constant (K = 10(-6) M) but different maximal binding capacities for the two lipoproteins (8 Cu(+2)/HDL as compared to 17 Cu(+2)/LDL). Given the size difference between HDL and LDL, these results imply that the maximal surface density of bound copper is at least 2-fold higher for HDL than for LDL. This difference may be responsible for the higher susceptibility of HDL to copper-induced oxidation in the presence of high copper concentrations. At relatively low copper concentrations, the kinetic profile of HDL oxidation was biphasic, similar to but more pronounced than the biphasic kinetics observed for the oxidation of LDL lipids at the same concentration of copper. Our results are consistent with the hypothesis that the first phase of rapid oxidation occurs via a tocopherol-mediated-peroxidation (TMP) mechanism. Accordingly, enrichment of HDL with tocopherol resulted in enhanced accumulation of hydroperoxides during the first phase of copper-induced oxidation. Notably, the maximal accumulation during the first phase decreased upon increasing the ratio of bound copper/HDL. This behavior can be predicted theoretically for peroxidation via a TMP mechanism, in opposition to autoaccelerated peroxidation. The possible pathophysiological significance of these findings is discussed.     

Expression and synthesis of TGFbeta1 is induced in macrophages by 9-oxononanoyl cholesterol, a major cholesteryl ester oxidation product

Within the broad variety of compounds generated via oxidative reactions in low density lipoproteins (LDL) and subsequently found in the atherosclerotic plaque, are aldehydes still esterified to the parent lipid and termed core-aldehydes. The most represented cholesterol core-aldehyde in LDL is 9-oxononanoyl cholesterol (9-ONC), an oxidation product of cholesteryl linoleate. Here we report that 9-ONC, at concentration actually detectable in biological material, significantly up-regulates the expression and the synthesis of the pro-fibrogenic cytokine transforming growth factor beta1 (TGFbeta1) by cultured macrophages. As previously demonstrated for other lipid oxidation products present in LDL, namely a biologically representative mixture of oxysterols and the unesterified aldehyde 4-hydroxynonenal, these effects on TGFbeta1 by 9-ONC further points to LDL lipid oxidation as a powerful source of pro-fibrogenic stimuli.     

Insulin-secreting beta-cell dysfunction induced by human lipoproteins

Diabetes is associated with significant changes in plasma concentrations of lipoproteins. We tested the hypothesis that lipoproteins modulate the function and survival of insulin-secreting cells. We first detected the presence of several receptors that participate in the binding and processing of plasma lipoproteins and confirmed the internalization of fluorescent low density lipoprotein (LDL) and high density lipoprotein (HDL) particles in insulin-secreting beta-cells. Purified human very low density lipoprotein (VLDL) and LDL particles reduced insulin mRNA levels and beta-cell proliferation and induced a dose-dependent increase in the rate of apoptosis. In mice lacking the LDL receptor, islets showed a dramatic decrease in LDL uptake and were partially resistant to apoptosis caused by LDL. VLDL-induced apoptosis of beta-cells involved caspase-3 cleavage and reduction in the levels of the c-Jun N-terminal kinase-interacting protein-1. In contrast, the proapoptotic signaling of lipoproteins was antagonized by HDL particles or by a small peptide inhibitor of c-Jun N-terminal kinase. The protective effects of HDL were mediated, in part, by inhibition of caspase-3 cleavage and activation of Akt/protein kinase B. In conclusion, human lipoproteins are critical regulators of beta-cell survival and may therefore contribute to the beta-cell dysfunction observed during the development of type 2 diabetes.     

Purification and characterization of bovine lipoproteins: resolution of high density and low density lipoproteins using heparin-Sepharose chromatography

The selective and reversible adsorption of bovine low density lipoproteins (LDL) by heparin-Sepharose has been exploited as the critical step in a procedure for the preparative isolation of very low density lipoproteins (VLDL)/chylomicrons, LDL, and high density lipoproteins (HDL) from bovine plasma. Molecular size exclusion chromatography and isopycnic density gradient separation steps are also involved in the method described. The resulting HDL and LDL fractions are free from contamination by one another as judged by electrophoretic mobility in agarose gels. The major lipid and apolipoprotein compositions of the three resolved lipoprotein classes have been determined.     

Increased oxidazability of plasma low density lipoprotein from patients with coronary artery disease

Oxidative modification of lipoproteins may play a crucial role in the pathogenesis of atherosclerosis. This study was designed to examine whether increased lipid peroxides and/or oxidative susceptibility of plasma lipoproteins occur in patients with coronary artery disease. The levels of lipid peroxides, estimated as thiobarbituric acid-reactive substances (TBARS), were significantly greater in the plasma and very low density lipoprotein (VLDL) of symptomatic patients with coronary artery disease than in those of healthy persons, but the TBARS levels of low density lipoprotein (LDL) and high density lipoprotein (HDL) showed insignificant difference between patients and normals. To evaluate the oxidative susceptibility of lipoproteins, we employed in vitro Cu²⁺ oxidation of lipoproteins monitored by changes in fluorescenece, TBARS level, trinitrobenzene sulfonic acid (TNBS) reactivity, apolipoprotein immunoreactivity and agarose gel electrophoretic mobility. While VLDL and LDL of normal controls were oxidazed at 5–10 μM Cu²⁺, pooled VLDL and LDL of patients with coronary artery disease were oxidized at 1–2.5 μM Cu²⁺, i.e., at relatively lowver oxidative stress. At 5 μM Cu²⁺, VLDL and LDL of patients with coronary artery disease still showed at faster oxidation rate, judged by the rate of fluorescence increase, higher TBARS level, less TNBS reactivity, greater change in apo B immunoreactivity and higher electrophoretic mobility than those of normal controls. However, the difference on the oxidizability of HDL was insignificant for patients vs. normals. In conclusion, we have shown that plasm VLDL and LDL of patients with coronary artery disease are more susceptible to in vitro oxidative modification than those of health persons. The data suggest that enhanced oxidizability of plasma lipoproteins may be important factor influencing the development of coronary artery disease.     

Protective effect of lipoproteins containing apoprotein A-I on Cu2+-catalyzed oxidation of human low density lipoprotein

Two apoprotein A-I (apoA-I)-containing lipoproteins, one containing apoA-I and apoA-II (LpA-I/A-II) and the other containing only apoA-I (LpA-I), were examined for their effect on Cu2+-mediated oxidation of low density lipoprotein (LDL). The presence of LpA-I or LpA-I/A-II prevented LDL oxidation when assessed by the electrophoretic mobility, apoprotein B fragmentation and amounts of thiobarbituric acid-reactive substances. The protection of LDL oxidation by these lipoproteins was effective for up to 6 h, with LpA-I being more active than LpA-I/A-II. Results from these in vitro model experiments raise a possibility that LpA-I may play a role in protecting LDL from Cu2+-mediated oxidation.     

Alterations in plasma lipoproteins and apolipoproteins in experimental allergic encephalomyelitis

Plasma lipoproteins were investigated during the active clinical phase of experimental allergic encephalomyelitis (EAE), a demyelinating disease of the central nervous system. Three groups of Lewis rats were compared: untreated controls, Freund's adjuvant-treated controls (FAC), and rats receiving one injection of myelin in Freund's adjuvant. After onset of clinical symptoms, 12 and 16 days after injection, there were higher concentrations of cholesterol and low and high density lipoproteins (LDL and HDL) in EAE plasma. The increase was due to apoE-containing HDL1 and HDL, according to density, particle size, and apolipoprotein compositions of isolated lipoproteins and immunoblots of whole plasmas after gradient gel electrophoresis. In EAE, the cholesterol-to-apoprotein ratio was increased and the low density lipoprotein distribution profile was shifted toward lower density. The Freund's adjuvant-treated control rats showed some changes qualitatively similar to those of EAE, albeit far smaller in magnitude. Changes in LDL in EAE might be related in part to lowered plasma very low density lipoproteins (VLDL); however, weight loss in control animals did not increase plasma cholesterol or apoE relative to apoA-I. Lesions in the central nervous system and/or activation of macrophages might be causally related to the large increase in plasma apoE. The major changes in apoE-containing lipoproteins are undoubtedly significant for the altered immune function in EAE.     

Macrophage colony-stimulating factor rapidly enhances beta-migrating very low density lipoprotein metabolism in macrophages through activation of a Gi/o protein signaling pathway

Previous studies have examined lipoprotein metabolism by macrophages following prolonged exposure (>24 h) to macrophage colony-stimulating factor (M-CSF). Because M-CSF activates several signaling pathways that could rapidly affect lipoprotein metabolism, we examined whether acute exposure of macrophages to M-CSF alters the metabolism of either native or modified lipoproteins. Acute incubation of cultured J774 macrophages and resident mouse peritoneal macrophages with M-CSF markedly enhanced low density lipoproteins (LDL) and beta-migrating very low density lipoproteins (beta-VLDL) stimulated cholesteryl [(3)H]oleate deposition. In parallel, M-CSF treatment increased the association and degradation of (125)I-labeled LDL or beta-VLDL without altering the amount of lipoprotein bound to the cell surface. The increase in LDL and beta-VLDL metabolism did not reflect a generalized effect on lipoprotein endocytosis and metabolism because M-CSF did not alter cholesterol deposition during incubation with acetylated LDL. Moreover, M-CSF did not augment beta-VLDL cholesterol deposition in macrophages from LDL receptor (-/-) mice, indicating that the effect of M-CSF was mediated by the LDL receptor. Incubation of macrophages with pertussis toxin, a specific inhibitor of G(i/o) protein signaling, had no effect on cholesterol deposition during incubation with beta-VLDL alone, but completely blocked the augmented response promoted by M-CSF. In addition, incubation of macrophages with the direct G(i/o) protein activator, mastoparan, mimicked the effect of M-CSF by enhancing cholesterol deposition in cells incubated with beta-VLDL, but not acetylated LDL. In summary, M-CSF rapidly enhances LDL receptor-mediated metabolism of native lipoproteins by macrophages through activation of a G(i/o) protein signaling pathway. Together, these findings describe a novel pathway for regulating lipoprotein metabolism.     

A dual role for lecithin:cholesterol acyltransferase (EC 2.3.1.43) in lipoprotein oxidation

Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme involved in lipoprotein metabolism. It mediates the transesterification of free cholesterol to cholesteryl ester in an apoprotein A-I-dependent process. We have isolated purified LCAT from human plasma using anion-exchange chromatography and characterized the extracted LCAT in terms of its molecular weight, molar absorption coefficient, and enzymatic activity. The participation of LCAT in the oxidation of very low density lipoproteins (VLDL) and low-density lipoproteins (LDL) was examined by supplementing lipoproteins with exogenous LCAT over a range of protein concentrations. LCAT-depleted lipoproteins were also prepared and their oxidation kinetics examined. Our results provide evidence for a dual role for LCAT in lipoprotein oxidation, whereby it acts in a dose-responsive manner as a potent pro-oxidant during VLDL oxidation, but as an antioxidant during LDL oxidation. We believe this novel pro-oxidant effect may be attributable to the LCAT-mediated formation of oxidized cholesteryl ester in VLDL, whereas the antioxidant effect is similar to that of chain-breaking antioxidants. Thus, we have demonstrated that the high-density lipoprotein-associated enzyme LCAT may have a significant role to play in lipoprotein modification and hence atherogenesis.     

Induction of interleukin 1 beta expression from human peripheral blood monocyte-derived macrophages by 9-hydroxyoctadecadienoic acid.

Oxidatively modified low density lipoproteins (LDL) have recently been proposed to play a role in atherogenesis by promoting foam cell formation and endothelial cell toxicity. The purpose of the present study was to determine whether modified LDL could also induce macrophage release of interleukin 1 beta (IL-1 beta), a cytokine which enhances vascular smooth muscle cell proliferation, another feature of the atherosclerotic process. LDL were oxidatively modified by incubation with either Cu2+ (Cu(2+)-LDL) or human peripheral blood monocyte-derived macrophages (M-LDL). Incubation of these modified LDL with macrophages (6 x 10(6) cells/culture) resulted in a dose-dependent induction of IL-1 beta release. At 300 micrograms protein/ml, Cu(2+)-LDL and M-LDL induced 422 and 333 pg of IL-1 beta/culture, respectively. Saponified Cu(2+)-LDL and M-LDL were shown to contain 9- and 13-hydroxyoctadecadienoic acid (HODE), lipid oxidation products of linoleate. When tested for activity in macrophage culture (3 x 10(6) cells/culture), it was found that 9-HODE and 13-HODE (final concentration 33 microM) induced the release of 122 and 43 pg of IL-1 beta/culture, respectively, whereas untreated cells released only 4 pg of IL-1 beta/culture. Incubation of macrophages with cholesteryl-9-HODE also induced IL-1 beta release; however, the degree of induction of IL-1 beta release by 9-HODE or its cholesteryl ester relative to modified LDL suggests that other components in oxidized LDL may also contribute to IL-1 beta induction. 9-HODE was rapidly taken up by macrophages, and the kinetics were similar to IL-1 beta release. A 1.5- to 6-fold increase in the level of IL-1 beta mRNA was detected as little as 3-h post-9-HODE treatment. The induction of IL-1 beta release from human monocyte-derived macrophages by 9-HODE and cholesteryl-9-HODE suggests a role for modified LDL, and its associated linoleate oxidation products, in vascular smooth muscle cell proliferation.     

Plasma and lipoprotein levels of tea catechins following repeated tea consumption

Epidemiological studies suggest that antioxidant flavonoids in tea may reduce the risk of cardiovascular disease, possibly via protection of low-density lipoproteins (LDL) against oxidation. However, the extent of absorption of tea flavonoids and their accumulation in LDL during regular consumption of tea is not clear. Therefore we investigated plasma and lipoprotein levels of catechins during tea consumption and the impact on LDL oxidizability ex vivo. Eighteen healthy adults consumed, in an incomplete balanced cross-over design, green tea, black tea, black tea with milk or water, one cup every 2 hr (eight cups/day) for three days. Blood samples were obtained in the mornings and evenings of each day. Plasma total catechin concentration was determined in all blood samples, and the distribution of catechins among lipoproteins was determined at the end of the third day (t = 60 hr). The resistance of LDL to copper-induced oxidation ex vivo was assessed before tea consumption and at t = 60 hr. Repeated tea consumption during the day rapidly increased plasma total catechin levels whereas they declined overnight when no tea was consumed. There was a gradual increase in plasma levels in the mornings (respectively, 0.08 microM vs. 0.20 microM on first and last day of black tea consumption) and evenings (respectively, 0.29 microM vs. 0.34 microM on first and last day of black tea consumption). Green tea catechins were mainly found in the protein-rich fraction of plasma (60%) and in high-density lipoproteins (23%). Although present in LDL, the concentration of catechins in LDL was not sufficient to enhance the resistance of LDL to oxidation ex vivo. Addition of milk to black tea did not affect any of the parameters measured. In conclusion, the present study shows that catechin levels in blood rapidly increase upon repeated tea consumption. The accumulation of catechins in LDL particles is not sufficient to improve the intrinsic resistance of LDL to oxidation ex vivo.     

The influence of oxidatively modified low density lipoproteins on expression of platelet-derived growth factor by human monocyte-derived macrophages

Platelet-derived growth factor (PDGF) is secreted by several cells that participate in the process of atherogenesis, including arterial wall monocyte-derived macrophages. Macrophages in human and non-human primate lesions have recently been demonstrated to contain PDGF-B chain protein in situ. In developing lesions of atherosclerosis, macrophages take up and metabolize modified lipoproteins, leading to lipid accumulation and foam cell formation. Oxidatively modified low density lipoproteins (LDL) have been implicated in atherogenesis and have been demonstrated in atherosclerotic lesions. The effects of the uptake of various forms of modified LDL on PDGF gene expression, synthesis, and secretion in adherent cultures of human blood monocyte-derived macrophages were examined. LDL oxidized in a cell-free system in the presence of air and copper inhibited the constitutive expression of PDGF-B mRNA and secretion of PDGF in a dose-dependent fashion. Oxidatively modified LDL also attenuated lipopolysaccharide-induced PDGF-B mRNA expression. These changes were unrelated to the mechanism of lipid uptake and the degree of lipid loading and were detectable within 2 h of exposure to oxidized LDL. The degree of inhibition of both basal and lipopolysaccharide-induced PDGF-B-chain expression increased with the extent of LDL oxidation. Monocyte-derived macrophages exposed to acetylated LDL or LDL aggregates accumulated more cholesterol than cells treated with oxidized LDL, but PDGF expression was not consistently altered. Thus, uptake of a product or products of LDL oxidation modulates the expression and secretion of one of the principal macrophage-derived growth factors, PDGF. This modulation may influence chemotaxis and mitogenesis of smooth muscle cells locally in the artery wall during atherogenesis.