Proinflammatory high-density lipoprotein results from oxidized lipid mediators in the pathogenesis of both idiopathic and associated types of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is characterized by abnormal elaboration of vasoactive peptides, endothelial cell dysfunction, vascular remodeling, and inflammation, which collectively contribute to its pathogenesis. We investigated the potential for high-density lipoprotein (HDL) dysfunction (i.e.

Isolevuglandin-type lipid aldehydes induce the inflammatory response of macrophages by modifying phosphatidylethanolamines and activating the receptor for advanced glycation endproducts.

Aims: Increased lipid peroxidation occurs in many conditions associated with inflammation. Because lipid peroxidation produces lipid aldehydes that can induce inflammatory responses through unknown mechanisms, elucidating these mechanisms may lead to development of better treatments for inflammatory diseases. We recently demonstrated that exposure of cultured cells to lipid aldehydes such as isolevuglandins (IsoLG) results in the modification of phosphatidylethanolamine (PE).

Transgenic 6F tomatoes act on the small intestine to prevent systemic inflammation and dyslipidemia caused by Western diet and intestinally derived lysophosphatidic acid.

We recently reported that levels of unsaturated lysophosphatidic acid (LPA) in the small intestine significantly correlated with the extent of aortic atherosclerosis in LDL receptor-null (LDLR⁻/⁻) mice fed a Western diet (WD). Here we demonstrate that WD increases unsaturated (but not saturated) LPA levels in the small intestine of LDLR⁻/⁻ mice and causes changes in small intestine gene expression. Confirmation of microarray analysis by quantitative RT-PCR showed that adding transgenic tomatoes expressing the apoA-I mimetic peptide 6F (Tg6F) to WD prevented many WD-mediated small intestine changes in gene expression.

A novel approach to oral apoA-I mimetic therapy.

Transgenic tomato plants were constructed with an empty vector (EV) or a vector expressing an apoA-I mimetic peptide, 6F. EV or 6F tomatoes were harvested, lyophilized, ground into powder, added to Western diet (WD) at 2.2% by weight, and fed to LDL receptor-null (LDLR(-/-)) mice at 45 mg/kg/day 6F.

High-density lipoprotein and 4F peptide reduce systemic inflammation by modulating intestinal oxidized lipid metabolism: novel hypotheses and review of literature.

Oxidized phospholipids are found in the vasculature of animal models of atherosclerosis, in human atherosclerotic lesions, and in other inflammatory diseases. Oxidized phospholipids cause vascular and nonvascular cells to initiate an inflammatory reaction. Metabolites of arachidonic acid, such as 12-hydroxyeicosatetraenoic acid, can mimic some of the inflammatory properties of oxidized phospholipids.

LXRα is uniquely required for maximal reverse cholesterol transport and atheroprotection in ApoE-deficient mice.

The liver X receptor (LXR) signaling pathway is an important modulator of atherosclerosis, but the relative importance of the two LXRs in atheroprotection is incompletely understood. We show here that LXRα, the dominant LXR isotype expressed in liver, plays a particularly important role in whole-body sterol homeostasis. In the context of the ApoE(-/-) background, deletion of LXRα, but not LXRβ, led to prominent increases in atherosclerosis and peripheral cholesterol accumulation.

HDL and cardiovascular disease: atherogenic and atheroprotective mechanisms.

The lipoprotein HDL has two important roles: first, it promotes reverse cholesterol transport, and second, it modulates inflammation. Epidemiological studies show that HDL-cholesterol levels are inversely correlated with the risk of cardiovascular events. However, many patients who experience a clinical event have normal, or even high, levels of HDL cholesterol.

Apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides inhibit tumor development in a mouse model of ovarian cancer.

We examined whether reduced levels of Apolipoprotein A-I (apoA-I) in ovarian cancer patients are causal in ovarian cancer in a mouse model. Mice expressing a human apoA-I transgene had (i) increased survival (P < 0.0001) and (ii) decreased tumor development (P < 0.

L-4F differentially alters plasma levels of oxidized fatty acids resulting in more anti-inflammatory HDL in mice.

To determine in vivo if L-4F differentially alters plasma levels of oxidized fatty acids resulting in more anti-inflammatory HDL. Injecting L-4F into apoE null mice resulted in a significant reduction in plasma levels of 15-HETE, 5-HETE, 13-HODE and 9-HODE. In contrast, plasma levels of 20-HETE were not reduced and plasma levels of 14,15-EET, which are derived from the cytochrome P450 pathway, were elevated after injection of L-4F.

Structure and function of HDL mimetics.

HDL mimetics have been constructed from a number of peptides and proteins with varying structures, all of which bind lipids found in HDL. HDL mimetics containing a peptide or protein have been constructed with as few as 4 and as many as 243 amino acid residues. Some HDL mimetics have been constructed with lipid but without a peptide or protein component.

Apolipoprotein A-I mimetic peptides.

Recent publications reveal the mechanism of action of apolipoprotein A-I (apoA-I) mimetic peptides to be the remarkable binding affinity that oxidized lipids have for these peptides compared with apoA-I. There was no difference in the binding affinity of oxidized lipids or in peptide efficacy in reducing inflammation and atherosclerosis in rabbits injected with peptides synthesized from all D- or all L-amino acids. The apoA-I mimetic peptide 4F increased the formation of pre-beta high-density lipoprotein, increased cholesterol efflux, and reduced lipoprotein oxidation in vitro; it increased antioxidants and vascular repair in type 1 diabetic rats; it improved vasodilation, oxidative stress, myocardial inflammation, and angiogenic potential in a mouse model of scleroderma; it reduced renal inflammation in low-density lipoprotein receptor-null mice fed a Western diet; it reduced arthritis in a rat model; it reduced adiposity, increased adiponectin levels, and improved insulin sensitivity in obese mice; and it improved high-density lipoprotein inflammatory properties in humans with coronary heart disease.

The role of dysfunctional HDL in atherosclerosis.

This review focuses on HDL function in modulating LDL oxidation and LDL-induced inflammation. Dysfunctional HDL has been identified in animal models and humans with chronic inflammatory diseases including atherosclerosis. The loss of antiinflammatory function correlated with a loss of function in reverse cholesterol transport.

Multiple indications for anti-inflammatory apolipoprotein mimetic peptides.

Apolipoprotein mimetic peptides dramatically reduce atherosclerosis in animal models, and may be an excellent mode of therapy to treat a variety of vascular inflammatory conditions, including atherosclerosis. Studies of apolipoprotein mimetic peptides in models of inflammatory disorders other than atherosclerosis, including viral influenza, asthma, chronic rejection after heart transplantation, sickle cell disease, scleroderma, diabetes, cognitive dysfunction and renal inflammation, suggest that apolipoprotein mimetic peptides may have efficacy in a wide range of inflammatory conditions.

Anti-inflammatory apoA-I-mimetic peptides bind oxidized lipids with much higher affinity than human apoA-I.

4F is an anti-inflammatory, apolipoprotein A-I (apoA-I)-mimetic peptide that is active in vivo at nanomolar concentrations in the presence of a large molar excess of apoA-I. Physiologic concentrations ( approximately 35 microM) of human apoA-I did not inhibit the production of LDL-induced monocyte chemotactic activity by human aortic endothelial cell cultures, but adding nanomolar concentrations of 4F in the presence of approximately 35 microM apoA-I significantly reduced this inflammatory response. We analyzed lipid binding by surface plasmon resonance.

Peptide Mimetics of Apolipoproteins Improve HDL Function.

Over the past decade evidence has accumulated that suggests that the anti-inflammatory properties of HDL may be at least as important as the levels of HDL-cholesterol. The recent failure of the torcetrapib clinical trails has highlighted the potential differences between HDL-cholesterol levels and HDL function. Agents to improve HDL function including HDL anti-inflammatory properties provide a new therapeutic strategy for ameliorating atherosclerosis and other chronic inflammatory conditions related to dyslipidemia.

Treatment with an apolipoprotein A-1 mimetic peptide in combination with pravastatin inhibits collagen-induced arthritis.

To evaluate the therapeutic potential of an apolipoprotein A-1 (apoA-1) mimetic peptide, D-4F, in combination with pravastatin in collagen-induced arthritis (CIA), syngeneic Louvain rats were immunized with type II collagen and randomized to vehicle control, D-4F monotherapy, pravastatin monotherapy, or D-4F + pravastatin combination therapy. Clinical arthritis activity was evaluated and radiographs, type II collagen antibody titers, cytokine/chemokine levels, and HDL function analysis were obtained. There was significant reduction in clinical severity scores in the high and medium dose D-4F + pravastatin groups compared to controls (p< or =0.

Apo A-1 mimetic peptides as atheroprotective agents in murine models.

The mouse has proven to be an excellent model for testing apolipoprotein mimetic peptides as agents to treat a variety of vascular inflammatory conditions including atherosclerosis, cognitive dysfunction associated with arteriole inflammation, chronic rejection of transplanted hearts, and scleroderma. The mechanism of action appears to relate to the ability of these peptides to preferentially bind pro-inflammatory oxidized lipids and is independent of the chirality of the peptides since peptides synthesized from either D- or L-amino acids appear to be equally effective.

High-density lipoprotein: antioxidant and anti-inflammatory properties.

The ability of high-density lipoprotein (HDL) to promote cholesterol efflux is an important component of its ability to protect against cardiovascular disease. In addition, the anti-inflammatory properties of HDL are important as well. As part of the innate immune system, HDL appears to have evolved to increase inflammation in the presence of an acute phase response but to inhibit inflammation in the absence of an acute phase response.

Lipoprotein inflammatory properties and serum amyloid A levels but not cholesterol levels predict lesion area in cholesterol-fed rabbits.

Rabbits on a 1% cholesterol diet received injections of vehicle with or without D-4F or L-4F. After 1 month, the percent of aorta with atherosclerotic lesions was 24 +/- 15% (vehicle), 10 +/- 6% (D-4F) (P < 0.01 vs.

Mechanisms of disease: proatherogenic HDL--an evolving field.

It is well known that, in large populations, HDL-cholesterol levels are inversely related to the risk of atherosclerotic clinical events; however, in an individual, the predictive value of an HDL-cholesterol level is far from perfect. As a result, other HDL-associated factors have been investigated, including the quality and function of HDL in contradistinction to the level of HDL-cholesterol. Regarding their quality, HDL particles are highly heterogeneous and contain varying levels of antioxidants or pro-oxidants, which results in variation in HDL function.

Potential clinical utility of high-density lipoprotein-mimetic peptides.

Purpose Of Review: To determine the potential clinical utility of high-density lipoprotein-mimetic peptides.

Recent Findings: Oral administration of D-4F together with pravastatin caused lesion regression in old apoE null mice. Administration of D-4F to low-density lipoprotein receptor null mice fed a Western diet reduced the association of myeloperoxidase with apoA-I and reduced the 3-nitrotyrosine content of apoA-I.

The double jeopardy of HDL.

The ability of high-density lipoprotein (HDL) to promote cholesterol efflux is thought to be important in its protection against cardiovascular disease. Anti-inflammatory properties of HDL have emerged as additional properties that may also be important. HDL appears to have evolved as part of the innate immune system functioning to inhibit inflammation in the absence of an acute phase response (APR) but functioning to increase inflammation in the presence of an APR.