Diminished rate of mouse peritoneal macrophage cholesterol efflux is not related to the degree of HDL glycation in diabetes mellitus.

The efflux of (14)C-cholesterol from mouse peritoneal macrophages mediated by in vivo and in vitro glycation of intact HDL(3) and by HDL(3) apolipoproteins was investigated. Cholesterol-laden cells were incubated a long time with HDL(3) from control subjects (C), poorly controlled diabetes mellitus patients (D) and with HDL C submitted to in vitro glycation (G), as well as with all their respectively isolated apolipoproteins. A diminished cholesterol efflux rate occurred in incubations with intact HDL(3) D but not with intact HDL(3)G or with apoHDL(3)C, G or D. The specific binding of (125)I-HDL(3)G to the cell receptor, obtained upon incubation in the absence and in the presence of excess unlabelled HDL(3), was lower than the control. The role of apoE secretion by cholesterol-laden macrophages on cholesterol efflux was analyzed by incubating apoE knockout and control mice macrophages with HDL C or HDL G: a lower cholesterol efflux was observed from apoE knockout macrophages but glycation of HDL(3) did not influence this process either. The diminished capacity to remove cholesterol by the HDL drawn from diabetic subjects must be attributed to other modifications of the lipoproteins, except for non enzymatic glycation. Thus, events that impair the cell cholesterol removal in diabetes mellitus are multifaceted.

Lipoproteins modify the macrophage uptake of triacylglycerol emulsion and of zymosan particles by similar mechanisms.

The uptake of lipids and formation of foam cells are key events in atherosclerosis and in eruptive xanthomata formation in primary hyperchylomicronemia. Here we have compared the influence of low density lipoprotein (LDL), oxidized LDL (oxLDL), high density lipoprotein (HDL), and delipidated HDL (apoHDL) on the uptake by macrophages of zymosan (an insoluble fraction of yeast cell walls) and of triglyceride-rich emulsion (EM) particles that resemble chylomicrons, but, like zymosan, are equally devoid of protein components. Zymosan internalization is known to occur through unspecific phagocytosis, whereas natural chylomicrons are taken up by several specific lipoprotein receptors. We found that phagocytosis is not promoted as much by oxLDL as by normal LDL. HDL-coated zymosan was found to be inert and apoHDL slightly enhanced phagocytosis. LDL and apoHDL promoted the uptake of EM while oxLDL and HDL significantly inhibited the uptake. Therefore, the data support that HDL, and not apoHDL, particles inhibit EM uptake. We concluded that by using lipoprotein-coated zymosan particles, we could demonstrate different biological effects of LDL, oxLDL, HDL, and apoHDL on macrophage phagocytosis and that this method could be useful to delineate components of the various lipoproteins important for the propagation or inhibition of the formation of foam cells.

Zymosan phagocytosis by mouse peritoneal macrophages is increased by apoHDL- and not by intact HDL-covered particles.

The uptake of lipids and lipoprotein particles by macrophages undergoes phagocytic activation and the formation of foam cells are key events in atherosclerosis. In this study we determined how intact high density lipoproteins (HDL) and apolipoproteins-HDL (removal of the lipid component from HDL, i.e., apoHDL) influence the phagocytosis of zymosan by mouse peritoneal macrophages. Zymosan particles preincubated together with lipoproteins or alone (control) were incubated with the macrophages. Phagocytosis activity was reported as the percent of macrophages that internalized three or more zymosan particles. HDL co-incubated with zymosan did not influence the over-all uptake of zymosan particles compared to apoHDL, which greatly enhanced the ability of the particle to be phagocytized (P<0.001). Part of this effect might be related to a greater binding of apoHDL to the particles compared to that of HDL (P<0.05). We conclude that this can be a useful method to study the ability of lipoproteins, including modified lipoproteins obtained from subjects with genetic forms of hyperlipidemia, to opsonize particles such as red blood cells and thus to investigate the processes that control the formation of foam cells and the mechanisms of atherogenesis.

Zymosan phagocytosis by mouse peritoneal macrophages is increased by apoHDL- and not by intact HDL-covered particles

The uptake of lipids and lipoprotein particles by macrophages undergoes phagocytic activation and the formation of foam cells are key events in atherosclerosis. In this study we determined how intact high density lipoproteins (HDL) and apolipoproteins-HDL (removal of the lipid component from HDL, i.e., apoHDL) influence the phagocytosis of zymosan by mouse peritoneal macrophages. Zymosan particles preincubated together with lipoproteins or alone (control) were incubated with the macrophages. Phagocytosis activity was reported as the percent of macrophages that internalized three or more zymosan particles. HDL co-incubated with zymosan did not influence the over-all uptake of zymosan particles compared to apoHDL, which greatly enhanced the ability of the particle to be phagocytized (P<0.001). Part of this effect might be related to a greater binding of apoHDL to the particles compared to that of HDL (P<0.05). We conclude that this can be a useful method to study the ability of lipoproteins, including modified lipoproteins obtained from subjects with genetic forms of hyperlipidemia, to opsonize particles such as red blood cells and thus to investigate the processes that control the formation of foam cells and the mechanisms of atherogenesis.

Plasma lipoproteins from patients with poorly controlled diabetes mellitus and "in vitro" glycation of lipoproteins enhance the transfer rate of cholesteryl ester from HDL to apo-B-containing lipoproteins.

Alterations in the reverse cholesterol transport system have been described in diabetic mellitus patients in several but not all studies. Furthermore, recently published investigations suggest that a faster "in vitro" transfer rate of cholesteryl ester from high density lipoproteins to apoB-containing lipoproteins could be solely ascribed to variation of the plasma lipoprotein composition and concentration in the diabetic state. The present study analysed the influence of lipoprotein glycation on the cholesteryl ester transfer protein-mediated transfer of esterified cholesterol from high density lipoprotein and its subfractions to lighter density lipoproteins. For this purpose two sets of "in vitro" experiments were carried out utilizing:1) plasma lipoproteins drawn from diabetic and from normal subjects and; 2) normal lipoproteins or partially purified cholesteryl ester transfer protein submitted to "in vitro" glycation. The transfer rate of 14C-cholesteryl ester labelled HDL subfractions to low or very low density lipoproteins was measured in all experiments. After incubations with plasma d > 1.21 g/ml or with purified cholesteryl ester transfer protein, apoB-containing lipoproteins were precipitated with a dextran sulfate/MgCl2 solution. The "in vitro" glycation of the partially purified cholesteryl ester transfer protein, markedly impaired its activity. However, greater transfer rates were observed when lipoproteins from diabetic individuals or the "in vitro" glycated lipoproteins were utilized. This effect was attributed to glycation of the protein component of HDL. In conclusion, lipoprotein glycation elicits an enrichment of the apoB-containing lipoproteins with cholesteryl ester that is likely related to the premature atherosclerosis in patients with poorly controlled diabetes.

Plasma cholesteryl ester synthesis, cholesteryl ester transfer protein concentration and activity in hypercholesterolemic women: effects of the degree of saturation of dietary fatty acids in the fasting and postprandial states.

Hypercholesterolemic women (n = 19) sequentially maintained on a long-term saturated (SAT) or a polyunsaturated (PUFA) fatty acid-rich diet, respectively, were studied in the fasting state and after a meal rich in SAT or PUFA. When apo B-containing lipoprotein was excluded from plasma the in vitro HDL-14C-cholesterol esterification rate was identical for the saturated (SAT) and polyunsaturated (PUFA) fatty acid diets, and did not increase during the postprandial period. Rates of transfer of 14C-cholesteryl ester to apo B-containing lipoproteins from HDL were also similar for both diets in the fasting state and increased to the same extent in the postprandial period in parallel with the rise in plasma triglycerides. When transfer data were related to the plasma concentration of apo B, the gain of cholesteryl ester by the triglyceride-containing particles (VLDL + LDL) also increased in the postprandial period to a similar extent for both diets. Cholesteryl ester transfer protein (CETP) concentration measured by radioimmunoassay was similar during both experimental diets, although greater in the postprandial period for the PUFA diet. The rate limiting factor for CETP-mediated transfer of HDL-derived cholesteryl ester (CE) was the plasma triglyceride concentration, that is, the content of triglycerides per lipoprotein particle and the quantity of TG-containing particles (VLDL + LDL). In contrast, the fatty acid composition of these particles had less effect on CETP-mediated CE transfer.