Role of PPAR-gamma in the modulation of CD36 and FcgammaRII induced by LDL with low and high degrees of oxidation during the differentiation of the monocytic THP-1 cell line.

Scavenger or Fcgamma receptors are important for capture and clearance of modified LDL particles by monocytes/macrophages. Uptake via scavenger receptors is not regulated by intracellular levels of cholesterol and in consequence, macrophages develop into foam cells in the arterial intima. The levels of scavenger receptor CD36 are increased in atherosclerotic lesions and there is evidence that some components of oxLDL auto-regulate the expression of this receptor. Fcgamma receptor expression is increased in cardiovascular diseases but it is not known weather their expression is regulated by oxLDL. The biological properties of oxLDLs vary depending on the degree of oxidation. In the present study we investigated the effect of LDL particles showing extensive or low oxidation (HoxLDL and LoxLDL) on the expression of CD36 and FcgammaRII in a human monocytic cell line (THP-1), differentiated or not to macrophage, and the involvement of PPARgamma. It was found that both forms of oxLDL are able to increase the expression of CD36 and FcgammaRII and that this effect is dependent on the degree of oxidation and of the stage of cell differentiation (monocyte or macrophage). We also showed that the increased expression of FcgammaRII is dependent on PPARgamma whereas that of the CD36 is independent of PPARgamma.

Soy protein containing isoflavones favorably influences macrophage lipoprotein metabolism but not the development of atherosclerosis in CETP transgenic mice.

The possibility that soy protein containing isoflavones influences the development of experimental atherosclerosis has been investigated in ovariectomized mice heterozygous for the human CETP transgene and for the LDL-receptor null allele (LDLr(+/-) CETP(+/-)). After ovariectomy at 8 wk of age they were fed a fat/cholesterol-rich diet for 19 wk and divided into three experimental groups: dietary unmodified soy protein containing isoflavones (mg/g of diet), either at low-dose (Iso Low, 0.272, n = 25), or at high-dose (Iso High, 0.535, n = 28); and the atherogenic diet containing an isoflavone-depleted alcohol-washed soy protein as a control group (n = 28). Aortic root lipid-stained lesion area (mean microm2 x 10(3) +/- SD) did not differ among Iso Low (12.3 +/- 9.9), Iso High (7.4 +/- 6.4), and controls (10.7 +/- 12.8). Autoantibody titers against plasma oxidized LDL did not differ among the experimental groups. Using the control mice as the reference value (100%), in vitro mouse peritoneal macrophage uptake of labeled acetylated LDL-cholesterol was lower in the Iso High (68%) than in the Iso Low (85%) group. The in vitro percent removal by exogenous HDL of labeled unesterified cholesterol from macrophages previously enriched with human [4- 14C]-cholesteryl oleate acetylated LDL was enhanced in the Iso High group (50%). In spite of these in vitro potentially antiatherogenic actions, soy protein containing isoflavones did not modify the average size of lipid-stained area in the aortic root.

The autoantibody repertoire against copper- or macrophage-modified LDL differs in normolipidemics and hypercholesterolemic patients.

We have analyzed the antibody repertoire from normo- and hypercholesterolemic subjects to investigate how it can be related to macrophage-dependent modification of low-density lipoproteins, in comparison to the commonly used copper-oxidized LDL. Preexisting natural antibodies in plasma from normo- and hypercholesterolemic individuals were tested for their reactivity against copper ion oxidized LDL and LDL modified by macrophages. A crosswise comparison between these two antigen preparations demonstrated a different antibody repertoire in normo- and hypercholesterolemic patients. This study suggest that the search for antibodies that can influence the progression or regression of an atherosclerotic process has to take into account the process by which LDL is modified, and the repertoire of antibodies that is generated in the normal population, in comparison to that with, or at risk for, coronary artery diseases.

Macrophages take up triacylglycerol-rich emulsions at a faster rate upon co-incubation with native and modified LDL: An investigation on the role of natural chylomicrons in atherosclerosis.

Chylomicrons play a role in atherosclerosis, however, because the mechanisms involved in the cell uptake of these particles are not fully understood, investigations were carried out using a radioactively labeled protein-free triacylglycerol-rich emulsion incubated with peritoneal macrophages obtained from normal and apoE-knockout mice. Experiments were done in the presence of substances that inhibit several endocytic processes: EDTA for low density lipoprotein receptor, fucoidan for scavenger receptor, cytochalasin B for phagocytosis, and a lipopolysaccharide for lipoprotein lipase. In addition, triacylglycerol-rich emulsions were also prepared in the presence of native or modified radioactively labeled low density lipoprotein particles that are known to accumulate in the arterial intima. Probucol was also used to prevent the possible role played by an antioxidant in triacylglycerol-rich emulsion uptake. We have shown that triacylglycerol-rich emulsion alone is taken up by a coated-pit-dependent mechanism, mediated by macrophage secretion of apolipoprotein E. Furthermore, native, aggregated, acetylated, and moderately macrophage-oxidized low density lipoprotein stimulate the uptake of a triacylglycerol-rich emulsion through several mechanisms such as an actin-dependent pathway, scavenger receptors, and lipolysis mediated by lipoprotein lipase. On the other hand, in spite of the interaction of low density lipoprotein forms with a triacylglycerol-rich emulsion, the cellular triacylglycerol-rich emulsion uptake is impaired by copper-oxidized low density lipoprotein, possibly due to its diminished affinity towards lipoprotein lipase. We have also shown that macrophages take up aggregated low density lipoprotein better than the acetylated or oxidized forms of low density lipoprotein.