Phospholipase A2 inhibitors in the treatment of atherosclerosis: a new approach moves forward in the clinic.

Phase II results of the trials of two phospholipase A2 inhibitors which may be of value in the treatment of atherosclerosis and cardiovascular disease have been reported in the past year. Darapladib (GlaxoSmithKline) is an inhibitor of lipoprotein-associated phospholipase A2 and varespladib (Anthera) inhibits several forms of the secreted phospholipase A2s. Despite the apparent similarity of mechanism, which is also built into the compounds' names, the role of the two types of phospholipase in atherogenesis is very different.

Oxidation of chylomicron remnant-like particles inhibits their uptake by THP-1 macrophages by apolipoprotein E-dependent processes.

The influence of the oxidative state of chylomicron remnants (CMR) on the mechanisms of their uptake and induction of lipid accumulation by macrophages derived from the human monocyte cell line, THP-1, during foam cell formation was investigated using chylomicron-remnant-like particles (CRLPs) at 3 different levels of oxidation. The oxidative state of CRLPs was varied by exposure to CuSO(4) (oxCRLPs) or incorporation of the antioxidant, probucol (pCRLPs) into the particles. oxCRLPs caused significantly less accumulation of triacylglycerol in the macrophages than CRLPs, and their rate of uptake was lower, while pCRLPs caused more lipid accumulation and were taken up faster.

The return of two old targets?

Once the physiological function of an enzyme is understood, a rationale for therapeutic intervention often becomes apparent. It is much harder to find synthetic inhibitors with the required specificity and safety. Preclinical biological data packages are not always predictive of the response in humans.

Novel candidate genes in unstable areas of human atherosclerotic plaques.

Objective: Comparison of gene expression in stable versus unstable atherosclerotic plaque may be confounded by interpatient variability. The aim of this study was to identify differences in gene expression between stable and unstable segments of plaque obtained from the same patient.

Methods And Results: Human carotid endarterectomy specimens were segmented and macroscopically classified using a morphological classification system.

Efflux of lipid from macrophages after induction of lipid accumulation by chylomicron remnants.

The fate of cholesterol and triacylglycerol taken up and accumulated by macrophages after exposure to chylomicron remnants was investigated using macrophages derived from the human monocyte cell line THP-1 and chylomicron remnant-like particles containing human apolipoprotein (apo) E (CRLPs) as the experimental model. In THP-1 macrophages lipid loaded with CRLPs and incubated with various cholesterol acceptors for 24 h, the mass of cholesterol and cholesteryl ester found in the cells was not changed by HDL, HDL3 or lipid-free ApoA-I, although it was decreased by 38% by ApoA-I-phosphatidylcholine vesicles (ApoA-I-PC). After loading of the macrophages with [3H]cholesterol-labelled CRLPs, only about 5% of the label was effluxed in 24 h in the absence of cholesterol acceptors, and this increased to about 10% with ApoA-I or PC only, and to about 30% with apoA-I-PC.

Characterisation of the lipoprotein structure in the St. Thomas' Mixed Hyperlipidaemic (SMHL) rabbit.

Familial combined hyperlipidaemia (FCHL) is a complex genetic disorder of unknown aetiology. Study of this human condition over many decades has been hampered by likely genetic heterogeneity. In order to find better phenotypic markers, we have characterised the structures of VLDL, IDL and LDL in the St.

The PPARdelta agonist GW0742X reduces atherosclerosis in LDLR(-/-) mice.

Several lines of evidence suggest a biological role for peroxisome proliferator-activated receptor (PPARdelta) in the pathogenesis of atherosclerosis. Administration of synthetic PPARdelta agonists to obese rhesus monkeys elevates serum high-density lipoprotein (HDL) cholesterol as a result of increased reverse cholesterol transport whilst in vitro studies have suggested a role for PPARdelta in lipid uptake into macrophages. Recent studies have found that PPARdelta depletion from macrophages in LDL receptor (LDLR(-/-)) mice decreases lesion area via modulation of the inflammatory status of the macrophage, an effect also seen on pharmacological activation of PPARdelta in vitro.

Short term arterial remodelling in the aortae of cholesterol fed New Zealand white rabbits shown in vivo by high-resolution magnetic resonance imaging - implications for human pathology.

High-resolution, non-invasive imaging methods are required to monitor progression and regression of atherosclerotic plaques. We investigated the use of MRI to measure changes in plaque volume and vessel remodelling during progression and regression of atherosclerosis in New Zealand White rabbits. Atherosclerotic lesions were induced in the abdominal aorta by balloon injury and cholesterol feeding.

Protection of chylomicron remnants from oxidation by incorporation of probucol into the particles enhances their uptake by human macrophages and increases lipid accumulation in the cells.

The effects of protection of chylomicron remnants from oxidation on their uptake and induction of lipid accumulation in macrophages were investigated using chylomicron remnant-like particles (CRLPs) containing the lipophilic antioxidant drug, probucol, and macrophages derived from the human monocyte cell line, THP-1. The total lipid content of THP-1 macrophages was markedly higher (x2.2) after 48 h of incubation of THP-1 macrophages with CRLPs containing probucol (pCRLPs) when compared to CRLPs without probucol, and this was because of increases in triacylglycerol (x2.

Differential effects of low-density lipoprotein and chylomicron remnants on lipid accumulation in human macrophages.

The effects of low-density lipoprotein (LDL) and chylomicron remnants on lipid accumulation in human monocyte-derived macrophages (HMDMs) and in macrophages derived from the human monocyte cell line THP-1 were compared. The HMDMs or THP-1 macrophages were incubated with LDL, oxidized LDL (oxLDL), chylomicron remnant-like particles (CMR-LPs), or oxidized CMR-LPs (oxCMR-LPs), and the amount and type of lipid accumulated were determined. As expected, the lipid content of both cell types was increased markedly by oxLDL but not LDL, and this was due to a rise in cholesterol, cholesteryl ester (CE), and triacylglycerol (TG) levels.

Chylomicron remnants and oxidised low density lipoprotein have differential effects on the expression of mRNA for genes involved in human macrophage foam cell formation.

The effects of chylomicron remnants (non-oxidised or oxidised) and oxidised low density lipoprotein (oxLDL) on the expression of mRNA for a wide range of genes believed to play a role in macrophage foam cell formation were compared using macrophages derived from the human monocyte cell line THP-1. Chylomicron remnant-like particles (CMR-LPs), oxidised CMR-LPs (oxCMR-LPs) and oxLDL were incubated with THP-1 macrophages, and the relative abundance of mRNA transcripts for genes involved in lipoprotein uptake, intracellular lipid metabolism, transport and storage and cholesterol efflux from macrophages was determined. The results show that CMR-LPs and oxLDL differ markedly in their effects on the expression of mRNA for a number of the genes tested.

Incorporation of lycopene into chylomicron remnant-like particles enhances their induction of lipid accumulation in macrophages.

Lipid accumulation in macrophages exposed to chylomicron remnant-like particles containing the dietary antioxidant lycopene was investigated. After incubation with THP-1 macrophages (48h), chylomicron remnant-like particles containing lycopene (lycCRLPs) as compared to those without (CRLPs) caused significantly more lipid accumulation in the cells, and this was due to increases in both the triacylglycerol (+100%) and cholesterol (+62%) content. In addition, expression of mRNA for diacylglycerol acyltransferase (DGAT), a key enzyme in triacylglycerol synthesis, was significantly decreased by lycCRLPs, but not CRLPs.

Repeated three-dimensional magnetic resonance imaging of atherosclerosis development in innominate arteries of low-density lipoprotein receptor-knockout mice.

Background: In vivo methods to evaluate the size and composition of atherosclerotic lesions in animal models of atherosclerosis would assist in the testing of antiatherosclerotic drugs. We have developed an MRI method of detecting atherosclerotic plaque in the major vessels at the base of the heart in low-density lipoprotein (LDL) receptor-knockout (LDLR(-/-)) mice on a high-fat diet.

Methods And Results: Three-dimensional fast spin-echo magnetic resonance images were acquired at 7 T by use of cardiac and respiratory triggering, with approximately 140- micro m isotropic resolution, over 30 minutes.

Lipoprotein-associated phospholipase A2: a target directed at the atherosclerotic plaque.

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is so named because it is found in human plasma largely associated with low-density lipoprotein (LDL). It is secreted by macrophages and able to hydrolyse oxidised fatty acids from oxidised phospholipids in LDL thereby releasing pro-atherogenic lysophosphatidylcholine and fatty acids. Inhibition of this enzyme activity was proposed to be antiatherogenic and this hypothesis has been confirmed both in vitro and in animal studies using specific inhibitors.