HDL lipid composition is profoundly altered in patients with type 2 diabetes and atherosclerotic vascular disease.

BACKGROUND AND AIMS: We have previously shown that the anti-inflammatory and anti-oxidant functions of HDL are impaired in T2D patients. In this study, we examined whether HDL from T2D patients contains elevated levels of oxidized fatty acids and whether those levels correlate with cardiovascular disease (CVD). METHODS AND RESULTS: HETEs and HODEs on HDL were determined by LC-MS/MS in 40 non-diabetic controls (ND), 40 T2D without CVD (D⁺CVD⁻) and 38 T2D with known history of CVD (D⁺CVD⁺). HDL oxidant index was evaluated by a cell-free assay using dichlorofluorescein. Twenty-six randomly selected subjects from the three groups underwent coronary calcium score evaluation (CAC). Major cardiovascular risk factors were similar among the groups. HETEs and HODEs content were significantly increased in HDL from D⁺CVD⁺ when compared to D⁺CVD⁻ and ND patients. HDL oxidant index was not different among the three groups; however, it was significantly higher in patients with CAC score >100 when compared to patients with CAC score <100. CONCLUSION: Patients with D⁺CVD⁻ and D⁺CVD⁺ are characterized by a severe, graded enrichment of oxidized fatty acids on HDL. In the present study, a loss of HDL function (as estimated by the HDL oxidant index) is observed only in patients with more advanced atherosclerosis.

ApoA-I mimetics favorably impact cyclooxygenase 2 and bioactive lipids that may contribute to cardiometabolic syndrome in chronic treated HIV.

OBJECTIVE: We investigated whether apolipoprotein A-I (apoA-I) mimetic peptides 4F and 6F can be a novel therapeutic strategy to reduce blood and gut bioactive lipids, proinflammatory effects of endotoxin (LPS) and aberrant activation of cyclooxygenase 2 (COX-2) as instigators of increased risk for cardiometabolic disease in chronic treated HIV. METHODS: We used two humanized murine models of chronic treated HIV infection (n = 109 mice) and gut explants from HIV infected (n = 10) persons to determine whether Tg6F and 4F attenuate in vivo and ex vivo increased blood and gut bioactive lipids (measured by mass spectrometry) and intestinal protein levels of COX-2 (measured by immunoassays) in chronic treated HIV. RESULTS: In these models of HIV, when compared to HIV-1 infected mice on antiretroviral therapy (ART) alone, oral Tg6F in combination with ART attenuated increases in plasma and gut bioactive lipids (and particularly COX lipids) and intestinal COX-2. 4F and Tg6F also reduced ex vivo production of COX-2 protein and associated secretion of bioactive lipids in gut explants from HIV-1 infected persons treated with LPS. CONCLUSION: ApoA-I mimetics favorably impact the proinflammatory effects of LPS, COX-2 and production of bioactive lipids that collectively drive gut and systemic inflammation in chronic treated HIV. Given prior experimental evidence that the proinflammatory effects of LPS, COX-2 and gut dysfunction contribute to cardiometabolic syndrome in chronic HIV, apoA-I mimetic peptides may be a novel therapy to treat cardiometabolic syndrome in chronic HIV.

Mevalonate metabolism: role of kidneys.

More than one-half of the amount of mevalonate that is metabolized by pathways not leading to sterols is accounted for by the action of the kidneys. Conversion of mevalonate in vivo to squalene and sterols in the kidneys is confined almost entirely to the proximal and distal convoluted tubules in the cortex. More sterol than squalene is synthesized from mevalonate not only in the liver but also in the kidney.

Receptor recognition of maleyl-albumin induces chemotaxis in human monocytes.

We demonstrate here that the exceptionally active maleyl-albumin receptor of human monocytes functions in vitro as a chemoattractant receptor. Chemotaxis of human monocytes occurs at an effective median dose of 3-4 microM maleyl-albumin, a concentration representing 1% of the total albumin in the adult human. Computerized analyses by LIGAND of the saturable binding of maleyl-albumin to human monocytes reveal two classes of binding sites, described by dissociation constants of 37 nM and 5.3 microM with maximal binding of 1.6 and 23 pmol maleyl-albumin/mg cellular protein, respectively. Chemotaxis of human monocytes thus occurs at concentrations of maleyl-albumin promoting binding to the lower-affinity sites. We propose that conformational isomers of albumin that are chemotactic may form in vivo and that albumin, in addition to receptor-independent plasma transport functions, may also play an important role in the receptor-mediated recruitment and accumulation of phagocytic cells at sites of inflammation and injury.

Effect of monocyte migration on low density lipoprotein transport across aortic endothelial cell monolayers.

Endothelial cell monolayers on polycarbonate filters present a barrier to low density lipoprotein (LDL) and albumin transport. These cells form a relatively tight monolayer as shown by measurements of electrical resistance across the monolayer (15 omega-cm2). Monocytes are able to migrate freely across the monolayers in response to chemotactic stimuli. Monocyte chemotaxis across the monolayer caused a marked increase in LDL and albumin transport across the monolayer in the direction of monocyte migration. However, transport in the opposite direction was not significantly increased. These results suggest that monocyte migration across the endothelium could lead to an increased LDL content of the intima.

Induction of heme oxygenase-1 inhibits the monocyte transmigration induced by mildly oxidized LDL.

Heme catabolic processes produce the antioxidants biliverdin and bilirubin, as well as the potent prooxidant free iron. Since these products have opposing effects on oxidative stress, it is not clear whether heme catabolism promotes or inhibits inflammatory processes, including atherosclerotic lesion formation. Heme oxygenase (HO) catalyzes the rate-limiting step of heme catabolism. We used cocultures of human aortic endothelial cells and smooth muscle cells to examine the possible role of HO in early atherosclerosis. Heme oxygenase-1 (HO-1), the inducible isoform of HO, was highly induced by mildly oxidized LDL, and augmented induction was observed with hemin pretreatment. This augmented HO-1 induction resulted in the reduction of monocyte chemotaxis in response to LDL oxidation. Conversely, inhibition of HO by a specific inhibitor, Sn-protoporphyrin IX, enhanced chemotaxis. Furthermore, pretreatment with biliverdin or bilirubin, the products of HO, reduced chemotaxis. Oxidized phospholipids in the mildly oxidized LDL appear to be responsible for HO-1 induction, since oxidized but not native arachidonic acid-containing phospholipids also induced HO-1. These results suggest that HO-1 induced by mildly oxidized LDL may protect against the induction of inflammatory responses in artery wall cells through the production of the antioxidants biliverdin and bilirubin.

Genetic control of inflammatory gene induction and NF-kappa B-like transcription factor activation in response to an atherogenic diet in mice.

A high fat, high cholesterol "atherogenic" diet induced considerably greater hepatic levels of conjugated dienes and expression of several inflammatory and oxidative stress responsive genes (JE, the mouse homologue of monocyte chemotactic protein-1, colony-stimulating factors, heme oxygenase, and members of the serum amyloid A family) in fatty streak susceptible C57BL/6 mice compared to fatty streak resistant C3H/HeJ mice. Since serum amyloid A proteins bind exclusively to HDL and influence the properties of HDL, serum amyloid A expression may contribute to the decrease in HDL levels seen in the susceptible strains. Induction of a similar set of genes was observed upon injection of minimally oxidized low density lipoprotein. The transcription factor NF-kappa B is known to be activated by oxidative stress and is involved in the transcriptional regulation of several of these genes. On the atherogenic diet the susceptible C57BL/6 mice exhibited significant NF-kappa B-like activation whereas the resistant C3H/HeJ mice exhibited little or no activation. These results are consistent with the hypothesis that the atherogenic diet resulted in the accumulation of oxidized lipids in certain tissues (e.g., liver and arteries) and the resulting inflammatory response to this oxidative stress was genetically determined.

Two distinct receptors account for recognition of maleyl-albumin in human monocytes during differentiation in vitro.

A comparison of the receptor-mediated interaction of malondialdehyde-low density lipoprotein and maleyl-albumin has been examined in human monocytes during differentiation in vitro. The recognition of both ligands by the scavenger receptor of these cells has been confirmed. We now report that human monocytes express a second cellular surface receptor for maleyl-albumin that is distinct from the scavenger receptor. The activity of the maleyl-albumin receptor, determined by both binding and lysosomal hydrolytic assays, substantially exceeds that of the scavenger receptor in freshly isolated monocytes. A dramatic and rapid decline in the activity of the maleyl-albumin receptor occurs within 72 to 96 h during differentiation in vitro. At day 7, while only 5-10% of the original activity of the maleyl-albumin receptor remains, it is similar to that of the maximally expressed scavenger receptor. Both the binding and hydrolysis of ligand mediated by the maleyl-albumin receptor are specifically inhibited by alpha-casein and alkaline-treated albumin; neither of these proteins is recognized by the scavenger receptor. The occurrence of the exceptionally active maleyl-albumin receptor on freshly isolated human monocytes suggests that it participates in processes necessary to the function of the cells that diminish in importance after differentiation of the monocytes into macrophages in vitro. Furthermore, while maleyl-albumin is a useful adjunct to studies of cellular events mediated by the scavenger receptor, the presence of a second receptor for maleyl-albumin must be taken into account as a potential contributing and complicating event.

Minimally modified low density lipoprotein-induced inflammatory responses in endothelial cells are mediated by cyclic adenosine monophosphate.

We have previously shown that minimally oxidized LDL (MM-LDL) activated endothelial cells to increase their interaction with monocytes but not neutrophils, inducing monocyte but not neutrophil binding and synthesis of monocyte chemotactic protein-1 and monocyte colony-stimulating factor (M-CSF). In the present studies we have examined the signaling pathways by which this monocyte-specific response is induced. Both induction of monocyte binding and mRNA levels for M-CSF by MM-LDL were not inhibited in protein kinase C-depleted endothelial cells. A number of our studies indicate that cAMP is the second messenger for the effects of MM-LDL cited above. Incubation of endothelial cells with MM-LDL caused a 173% increase in intracellular cAMP levels. Agents which increased cAMP levels, including cholera toxin, pertussis toxin, dibutyryl cAMP, and isoproterenol mimicked the actions of MM-LDL. Agents which elevated cAMP were also shown to activate NF kappa B, suggesting a role for this transcription factor in activation of monocyte-endothelial interactions. Although endothelial leukocyte adhesion molecule (ELAM) mRNA synthesis can be regulated by NF kappa B, ELAM was not expressed and ELAM mRNA was only slightly elevated in response to MM-LDL. We present evidence that induction of neutrophil binding by LPS is actually suppressed by agents that elevated cAMP levels.

A new antiinflammatory compound, leumedin, inhibits modification of low density lipoprotein and the resulting monocyte transmigration into the subendothelial space of cocultures of human aortic wall cells.

Addition of leumedin, N-[9H-(2,7-dimethylfluorenyl-9-methoxy) carbon]-L-leucine at 30-60 microM together with LDL almost completely prevented the induction of monocyte chemotactic protein mRNA, reduced monocyte chemotactic protein 1 levels by 84%, and inhibited monocyte migration into the subendothelial space of cocultures of human aortic wall cells by < or = 98%. LDL incubated with leumedin formed a stable complex that remained intact even after refloating in an ultracentrifuge. Leumedin at 50 microM did not change conjugated diene formation during coculture modification of LDL or Cu++ catalyzed oxidation of LDL. Unlike LDL from control rabbits, LDL isolated from rabbits that were injected with 20 mg/kg leumedin was remarkably resistant to modification by the coculture and did not induce monocyte migration to a significant degree. Moreover, HDL isolated from rabbits injected with leumedin was far more effective in protecting against LDL modification by the artery wall cocultures than HDL from control rabbits. We conclude that leumedins can associate with lipoproteins in vivo, rendering LDL resistant to biological modification and markedly amplifying the protective capacity of HDL against in vitro LDL oxidation by artery wall cells.

Minimally modified low density lipoprotein is biologically active in vivo in mice.

Minimally modified low density lipoprotein (MM-LDL), derived by mild iron oxidation or prolonged storage at 4 degrees C, has been shown to induce certain inflammatory responses in vascular cells in tissue culture. These include induction of monocyte (but not neutrophil) adherence to endothelial cells (EC), induction of EC production of colony stimulating factors (CSF), and induction of EC and smooth muscle cell production of monocyte chemotactic protein (MCP-1). To test for biologic activity in vivo, microgram quantities of MM-LDL were injected into mice, sera were assayed for CSF activity, and tissues were subjected to Northern analysis. After injection of MM-LDL, CSF activity increased approximately 7-26-fold but remained near control levels after injection of native LDL. Essentially all of the induced CSF activity was due to macrophage CSF as judged by antibody inhibition. Injection of MM-LDL into a mouse strain (C3H/HeJ) that is resistant to bacterial LPS gave similar results, indicating that the induction of CSF was not due to contaminating LPS and suggesting that there are differences in the pathways by which LPS and MM-LDL trigger cytokine production. In addition, after injection of MM-LDL, mRNA for JE, the mouse homologue of MCP-1, was markedly induced in various tissues, but was not induced after injection of native LDL. We conclude, therefore, that MM-LDL is biologically active in vivo and may contribute to the early stages of atherosclerosis by acting as an inflammatory agent.

Lipid-induced changes in intracellular iron homeostasis in vitro and in vivo.

Iron promotes cellular damage via its capacity to catalyze hydroxyl radical formation and by peroxidation of unsaturated lipids. The major cellular iron storage depot, ferritin, acts as a critical antioxidant defense by sequestering unbound or "free" iron, limiting its participation in damaging oxidative reactions. In this study, we investigated the relationship between LDL modified by artery wall cells and the regulation of intracellular free iron levels in the mouse model and in a human aortic endothelial and smooth muscle cell coculture system. We found in response to an atherogenic diet, fatty streak-resistant C3H/HeJ mice exhibited higher levels of liver apoferritin and lower intracellular concentrations of free iron than did fatty streak-susceptible C57 BL/6J mice. Also, ferritin repressor protein mRNA was not significantly suppressed after 15 wk on the atherogenic diet in female C57BL/6J mice, which exhibit the most extensive fatty streak formation, but was significantly reduced in C3H/HeJ mice. Iron loading of coculture cells resulted in elevations of cellular free iron and enhanced LDL-induced monocyte transmigration. Pretreatment of cells with apoferritin completely abolished iron-induced LDL modification. Addition of LDL to cocultures resulted in elevations in lipid peroxidation products, intracellular free iron, apoferritin mRNA expression, and apoferritin synthesis, suggesting a possible relationship between the oxidative modification of LDL and iron metabolism.

Genetic evidence for a common pathway mediating oxidative stress, inflammatory gene induction, and aortic fatty streak formation in mice.

In a previous survey of inbred mouse strains on an atherogenic diet, we observed that the susceptibility to aortic atherosclerotic lesion formation was associated with the accumulation of lipid peroxidation products, induction of inflammatory genes, and the activation of NF-kB-like transcription factors (Liao, F., A. Andalibi, F. C. deBeer, A. M. Fogelman, and A.J. Lusis. 1993. J. Clin. Invest. 91:2572-2579). We hypothesized that the inflammation-related processes were stimulated by oxidized lipids, since injection of minimally oxidized LDL (MM-LDL) activated the same set of genes. We now report that the induction of inflammatory genes and activation of NF-kB-like transcription factors cosegregate with aortic atherosclerotic lesion formation in BXH recombinant inbred strains derived from parental C57BL/6J (susceptible) and C3H/HeJ (resistant) mice. In addition, the accumulation of hepatic conjugated dienes exhibited a significant correlation with inflammatory gene activation. These results provide strong evidence for the role of inflammatory mediators inducible by oxidative stress in atherogenesis. They also suggest that a major gene contributing to aortic lesion development in this mouse model, designated Ath-1, may control either the accumulation of lipid peroxides in tissues or the cellular responses to such lipid peroxides.

Genetic-dietary regulation of serum paraoxonase expression and its role in atherogenesis in a mouse model.

In an effort to identify genetic factors contributing to atherogenesis, we have studied inbred strains of mice that are susceptible (C57BL/6J) and resistant (C3H/HeJ) to diet-induced aortic fatty streak lesions. When maintained on a low-fat diet, HDL isolated from both strain C57BL/6J (B6) and C3H/HeJ (C3H) mice protect against LDL oxidation in a coculture model of the artery wall. However, when maintained on an atherogenic diet high in fat and cholesterol, the HDL isolated from B6 mice lose the capacity to protect, whereas HDL from C3H mice protect equally well. Associated with the loss in the ability of HDL to protect is a decrease in the activity of serum paraoxonase, a serum esterase carried on HDL that has previously been shown to protect against LDL oxidation in vitro. The levels of paraoxonase mRNA decreased in B6 mice upon challenge with the atherogenic diet but increased in C3H, indicating that paraoxonase production is under genetic control. In a set of recombinant inbred strains derived from the B6 and C3H parental strains, low paraoxonase mRNA levels segregated with aortic lesion development, supporting a role for paraoxonase in atherogenesis.

Monocyte migration into the subendothelial space of a coculture of adult human aortic endothelial and smooth muscle cells.

Human aortic endothelial cells (EC) and smooth muscle cells (SMC) were isolated and used to form a multilayer of EC-SMC separated by a layer of collagen. SMC and/or collagen layers exerted minimal effects on Na+ transport but impeded the transport of LDL. The presence of an endothelial monolayer markedly reduced the transport of Na+ and LDL. When monocytes were presented to the complete coculture, in the absence of added chemoattractant, one monocyte entered the subendothelial space for every one to three EC present. In contrast, neither collagen nor SMC plus collagen nor EC plus collagen induced comparable monocyte migration. Despite massive migration of monocytes into the coculture, no significant alteration in Na+ transport was observed. LDL transport into the preparation during massive monocyte migration increased modestly, but this was far less than the amount of LDL transported in the absence of an endothelial monolayer. We conclude that (a) the endothelial monolayer was the principal permeability barrier, (b) a substantial migration of monocytes occurred in the absence of added chemoattractant when both EC and SMC were present in the coculture, (c) endothelial barrier function was largely maintained after monocyte migration; and (d) these experiments indicate the need to study all three cell types (monocytes, EC, and SMC) together to understand the complex interactions that occur between these cells.

Low density lipoproteins transfer bacterial lipopolysaccharides across endothelial monolayers in a biologically active form.

Rabbit aortic endothelial cells (RAECs) were grown on micropore filters in a device that allowed in situ determination of transendothelial electrical resistance (TEER). Incubation of confluent RAEC monolayers with 2 ng.ml-1 of bacterial LPS for 3 h did not change the protein content or the number of cells on the filters, but resulted in a marked decline in TEER (from 14.1 +/- 0.9 to 5.1 +/- 0.6 omega.cm2) and a significant increase in LDL transport across the monolayers (from 154 +/- 13 to 456 +/- 41 ng. h-1 per cm2). In contrast, exposure of RAEC monolayers for 3 d to as much as 5 micrograms.ml-1 of LPS complexed to LDL (LPS-LDL) did not alter the TEER or LDL transport. LPS-LDL was transported across the monolayers at the same rate as LDL. While microgram quantities of LPS complexed to LDL did not disrupt the integrity of the endothelial monolayer, incubation of RAECs with transported LPS-LDL at concentrations of 25-100 ng LPS.ml-1 resulted in a two- to ninefold increase in the secretion of monocyte chemotactic activity by these cells. Incubation of rabbit aortic smooth muscle cells with transported LPS-LDL at concentrations of 25-100 ng LPS.ml-1 resulted in a two- to threefold increase in the secretion of monocyte chemotactic activity. We propose that LDL protects endothelial cells from the acute toxicity of LPS but the resulting complexes are transported across the endothelium in a biologically active form that can initiate an inflammatory response.

Interaction of monocytes with cocultures of human aortic wall cells involves interleukins 1 and 6 with marked increases in connexin43 message.

Medium from cocultures of human aortic endothelial cells (HAEC) and smooth muscle cells (HASMC) taken from the same donor contained approximately two- to fourfold more macrophage colony-stimulating factor, granulocyte/macrophage colony-stimulating factor, and up to 5.1-fold more transforming growth factor beta than could be accounted for by the sum of the activities of media from equivalent numbers of HAEC and HASMC cultured separately. After pulse labeling, immunoprecipitated [35S]fibronectin and [14C]collagen were also found to be substantially increased in the coculture compared to the sum of HAEC and HASMC cultured separately. The cocultivation of HAEC and HASMC resulted in a 2.7-fold increase in connexin43 messenger RNA. When direct physical contact between HAEC and HASMC was prevented by a membrane that was permeable to medium, the levels of [35S]fibronectin and [14C]collagen in the coculture were significantly reduced. Monocytes cultured alone contained low levels of [35S]fibronectin and [14C]collagen but when added to the coculture there was up to a 22-fold increase in [35S]fibronectin and a 1.9-fold increase in [14C]collagen compared to the coculture alone. The increase in fibronectin was prevented in the presence of neutralizing antibody to interleukin 1 and antibody to interleukin 6 by 45% and 67%, respectively. Addition of monocytes to cocultures also induced the levels of mRNA for connexin43 by 2.8-fold. We conclude that the interaction of HAEC, HASMC, and monocytes in coculture can result in marked increases in the levels of several biologically important molecules and that increased gap junction formation between the cells and interleukins 1 and 6 may be partially responsible for these changes.

Role of the GRO family of chemokines in monocyte adhesion to MM-LDL-stimulated endothelium.

We have previously shown that treatment of endothelial cells with minimally modified LDL (MM-LDL) induces the binding of monocytes to unknown endothelial receptor molecules. We now report that a member of the GRO family of chemokines plays a role in MM-LDL-induced monocyte binding. A cDNA library made from rabbit aortic endothelial cells (RAEC) treated with MM-LDL was expression screened for molecules inducing binding of a human monocyte cell line (THP-1). A cDNA was isolated with 75% homology to GRO. GRO mRNA levels were significantly elevated after exposure of RAEC or human aortic endothelial cells (HAEC) to MM-LDL. HAEC treated with MM-LDL displayed an increase in a surface-associated protein that bound to antibody against GRO despite low levels of GRO in the medium. Antibody to GRO significantly inhibited the binding of monocytes to MM-LDL-treated RAEC and HAEC. The increase in GRO expression and monocyte binding were reduced by incubating MM-LDL-treated endothelial cells with heparin (in a method that releases heparan sulfate bound molecules from the cell surface). These results suggest that GRO related chemokines are bound to the surface of MM-LDL-treated endothelial cells and may contribute to the monocyte adhesion induced by MM-LDL.

Recipient mononuclear cell recognition and adhesion to graft endothelium after human cardiac transplantation. Lymphocyte recognition leads to monocyte adhesion.

Transendothelial migration of mononuclear cells is crucial in the development of allograft rejection and transplant coronary disease. Adhesion of circulating cells to endothelium is the initial step in transendothelial migration. Human aortic endothelial cell cultures were established from aortic tissue harvested at the time of organ donation for cardiac transplantation which allowed specific recipient mononuclear cell-graft endothelial interactions to be studied. Confluent untreated endothelial cells were incubated with recipient mononuclear cells for 15 min to assess adhesion. Adhesion of recipient mononuclear cells to endothelium derived from their graft was threefold higher than adhesion to nonspecific endothelium (93 +/- 20 vs. 30 +/- 11 cells/high power field, P < 0.005). Graft-specific adhesion was inhibited by preincubation of the endothelium with antibodies to class I HLA (34 +/- 16 cells/high power field, P < 0.005). Immunofluorescence performed after adhesion showed that 73 +/- 6% of both specific and nonspecific adherent cells were monocytes. The use of purified lymphocyte and monocyte preparations showed that graft-specific lymphocytes induce unrelated monocytes to become adherent. These results suggest that lymphocytes are primed in vivo to recognize endothelium derived from their graft which leads to a rapid increase in lymphocyte and monocyte adhesion. Such allo-recognition may involve endothelial class I HLA molecules.

Overexpression of apolipoprotein AII in transgenic mice converts high density lipoproteins to proinflammatory particles.

Previous studies showed that transgenic mice overexpressing either apolipoprotein AI (apoAI) or apolipoprotein AII (apoAII), the major proteins of HDL, exhibited elevated levels of HDL cholesterol, but, whereas the apoAI-transgenic mice were protected against atherosclerosis, the apoAII-transgenic mice had increased lesion development. We now examine the basis for this striking functional heterogeneity. HDL from apoAI transgenics exhibited an enhanced ability to promote cholesterol efflux from macrophages, but HDL from apoAII transgenics and nontransgenics were not discernibly different in efflux studies. In contrast with HDL from nontransgenics and apoAI transgenics, HDL from the apoAII transgenics were unable to protect against LDL oxidation in a coculture model of the artery wall. Furthermore, HDL taken from apoAII-transgenic mice, but not HDL taken from either the apoAI transgenics or nontransgenic littermate controls, by itself stimulated lipid hydroperoxide formation in artery wall cells and induced monocyte transmigration, indicating that the apoAII-transgenic HDL were in fact proinflammatory. This loss in the ability of the apoAII-transgenic HDL to function as an antioxidant/antiinflammatory agent was associated with a decreased content of paraoxonase, an enzyme that protects against LDL oxidation. Reconstitution of the apoAII transgenic HDL with purified paraoxonase restored both paraoxonase activity and the ability to protect against LDL oxidation. We conclude that overexpression of apoAII converts HDL from an anti- to a proinflammatory particle and that paraoxonase plays a role in this transformation.