Lipoprotein Use Research Articles

Human lipoproteins have divergent neutralizing effects on E. coli LPS, N. meningitidis LPS, and complete Gram-negative bacteria

The use of lipoproteins has been suggested as a treatment for Gram-negative sepsis because they inhibit lipopolysaccharide (LPS)-mediated cytokine production. However, little is known about the neutralizing effects of lipoproteins on cytokine production by meningococcal LPS or whole Gram-negative bacteria. We assessed the neutralizing effect of LDLs, HDLs, and VLDLs on LPS- or whole bacteria-induced cytokines in human mononuclear cells. A strong inhibition of Escherichia coli LPS-induced interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, and IL-10 by LDL and HDL was seen, whereas VLDL had a less pronounced effect. In contrast, Neisseria meningitidis LPS, in similar concentrations, was neutralized much less effectively than E. coli LPS. Effective neutralization of meningococcal LPS required a longer interaction time, a lower concentration of LPS, or higher concentrations of lipoproteins. The difference in neutralization was independent of the saccharide tail, suggesting that the lipid A moiety accounted for the difference. Minimal neutralizing effects of the lipoproteins were observed on whole E. coli or N. meningitidis bacteria under all conditions tested. These results indicate that efficient neutralization of LPS depends on the type of LPS, but a sufficiently long interaction time, a low LPS concentration, or high lipoprotein concentration also inhibited cytokines by the less efficiently neutralized N. meningitidis LPS. Irrespective of these differences, whole bacteria showed no neutralization by lipoproteins.

Hyperlipoproteinemia enhances susceptibility to acute disseminated Candida albicans infection in low-density-lipoprotein-receptor-deficient mice.

Recent studies have suggested the use of lipoproteins as an adjuvant treatment of lethal gram-negative infections. However, other important microorganisms for the etiology of sepsis, such as Candida species, grow better in lipid-rich environments. We investigated the effect of hyperlipoproteinemia on systemic candidiasis in low-density-lipoprotein-receptor-deficient (LDLR-/-) mice, in which the loss of the receptor results in a seven- to ninefold-higher plasma LDL level than that in their wild-type littermates (C57BL/6J). LDLR-/- mice died earlier, and the outgrowth of Candida albicans in the kidneys and livers of LDLR-/- mice was significantly higher compared with that of controls. After infection, circulating cytokine concentrations were significantly higher in LDLR-/- mice. In vitro, C. albicans grew better in plasma samples of LDLR-/- mice than in control plasma samples and peritoneal macrophages of LDLR-/- mice challenged with heat-killed C. albicans produced more cytokines than did those of controls. This latter phenomenon was probably due to increased binding of yeast cells to macrophages of LDLR-/- mice. These data suggest that hyperlipoproteinemia is deleterious in systemic candidiasis.

Study of LDL and acetylated LDL endocytosis by mononuclear cells in HIV infection

Activated lymphocytes have a high level of low density lipoprotein (LDL) uptake as compared to resting lymphocytes, whereas scavenger receptors for acetylated LDL (Ac-LDL) are expressed on limited number of immune cells, i.e., monocytes/macrophages. The endocytosis of LDL and Ac-LDL by mononuclear cells was studied during in vitro and in vivo HIV infection, in order to use LDL and Ac-LDL as carriers of antiviral and/or immunomodulatory drugs towards lymphocytes and monocytes. The uptake of LDL and Ac-LDL was analyzed by cytofluorimetry. LDL endocytosis in PHA/IL2-activated lymphocytes was higher than in resting lymphocytes. In vitro HIV infection of PHA/IL2-activated lymphocytes did not alter the high LDL endocytosis in lymphocytes, CD4 + and CD8 + cells. In a group of 12 symptomatic patients there was no alteration of LDL endocytosis in lymphocytes, CD4 and CD8 lymphocytes. In another group of 23 individuals, the Ac-LDL endocytosis mediated by CD14 + monocytes was unaltered in asymptomatic patients ( n = 6) and in some symptomatic patients ( n = 6, CD14 +cells > 100/mm 3). On the contrary, in other symptomatic patients ( n = 11, CD14 +cells < 100/mm 3), the number of Ac-LDL + CD14 + cells decreased, whereas their efficiency of Ac-LDL endocytosis increased as compared to those of other HIV + patients. In conclusion, the use of lipoproteins as carriers to increase the drug delivery to CD4 + lymphocytes and to CD14 + monocytes can be envisaged, since: (i) the LDL endocytosis was not impaired in CD4 lymphocytes of HIV + patients, and (ii) the Ac-LDL uptake by monocytes was altered only in some patients of stage IV.

Localization of prostaglandin F2 alpha inhibition of lipoprotein use by bovine luteal cells.

Prostaglandin F2 alpha (PGF2 alpha) inhibits lipoprotein-stimulated progesterone production by bovine luteal cells in vitro and the objective of this study was to localize the site of action of PGF2 alpha. Cultured bovine luteal cells were treated with PGF2 alpha for seven days, and then with either lipoproteins or 25-hydroxycholesterol in the presence of aminoglutethimide (which inhibits cholesterol side-chain cleavage) for the final 48 h. The effects of PGF2 alpha on progesterone production, cellular cholesterol content, mitochondrial cholesterol content and cholesterol side-chain cleavage activity were determined. As expected, PGF2 alpha inhibited (P less than 0.05) lipoprotein-stimulated progesterone production. However, PGF2 alpha did not inhibit low-density lipoprotein-stimulated, or high density lipoprotein-stimulated, increases in cellular cholesterol (P less than 0.05) or inhibit lipoprotein-induced increases in mitochondrial cholesterol content (P less than 0.05). Additionally, cholesterol content of mitochondria increased (P less than 0.05) in the presence of PGF2 alpha alone. To determine if the PGF2 alpha-induced inhibition of steroidogenesis occurred at, or after, the side-chain cleavage reaction, we treated cells with the readily diffusable sterol, 25-hydroxycholesterol. Prostaglandin F2 alpha did not inhibit 25-hydroxycholesterol-stimulated progesterone production (P less than 0.05). Prostaglandin F2 alpha may therefore exert its luteolytic effect at a site after cholesterol transport to the mitochondria but before cholesterol side-chain cleavage.

ChemInform Abstract: LIPOPROTEINS AS POTENTIAL SITE‐SPECIFIC DELIVERY SYSTEMS FOR DIAGNOSTIC AND THERAPEUTIC AGENTS

Despite the paucity of literature dealing with the effect of plasma lipoproteins upon drug disposition, evidence is accumulating that shows that these macromolecular complexes can play important roles in the absorption and transport of lipid-soluble agents. Moreover, preliminary studies have demonstrated that radiotracers can be directed to specific tissues by prior incorporation into the hydrophobic core of specific lipoproteins. Although these studies offer encouragement for the possible use of lipoproteins in the site-specific delivery of radiopharmaceuticals that are used in tracer doses, the use of lipoproteins in the transport of drugs at pharmacological concentrations represents a much greater challenge. Nothing is known at this time about the saturation kinetics of drug incorporation into lipoproteins or partially delipidated lipoproteins. Nor is there any assurance that drug-laden lipoproteins will participate in receptor-mediated uptake processes similar to native lipoproteins. Moreover, receptor-mediated uptake of lipoproteins is a saturable process and may not permit attainment of sufficient drug concentrations within cells. It could be argued, however, that receptor-mediated uptake could be enhanced by prior treatment with hypocholesterolemic drugs as has been shown for cholestyramine. In any event, the possible use of lipoproteins for the site-specific delivery of intravenously administered radiodiagnostics or highly potent drugs (e.g., anticancer agents) appears promising. Only the results of ongoing studies will determine the practicality of this approach.

Lipoproteins as potential site-specific delivery systems for diagnostic and therapeutic agents.

Despite the paucity of literature dealing with the effect of plasma lipoproteins upon drug disposition, evidence is accumulating that shows that these macromolecular complexes can play important roles in the absorption and transport of lipid-soluble agents. Moreover, preliminary studies have demonstrated that radiotracers can be directed to specific tissues by prior incorporation into the hydrophobic core of specific lipoproteins. Although these studies offer encouragement for the possible use of lipoproteins in the site-specific delivery of radiopharmaceuticals that are used in tracer doses, the use of lipoproteins in the transport of drugs at pharmacological concentrations represents a much greater challenge. Nothing is known at this time about the saturation kinetics of drug incorporation into lipoproteins or partially delipidated lipoproteins. Nor is there any assurance that drug-laden lipoproteins will participate in receptor-mediated uptake processes similar to native lipoproteins. Moreover, receptor-mediated uptake of lipoproteins is a saturable process and may not permit attainment of sufficient drug concentrations within cells. It could be argued, however, that receptor-mediated uptake could be enhanced by prior treatment with hypocholesterolemic drugs as has been shown for cholestyramine. In any event, the possible use of lipoproteins for the site-specific delivery of intravenously administered radiodiagnostics or highly potent drugs (e.g., anticancer agents) appears promising. Only the results of ongoing studies will determine the practicality of this approach.

Transfer of plasma lipoprotein components and of plasma proteins into aortas of cholesterol-fed rabbits. Molecular size as a determinant of plasma lipoprotein influx.

The arterial influx of esterified and free cholesterol from low density lipoproteins and very low density lipoproteins in 20 hypercholesterolemic rabbits was measured simultaneously by the use of lipoproteins labeled in vivo with [3H]- and [14C]-cholesterol. The simultaneous arterial influx of either [3H]-leucine-labeled very low density lipoproteins, low density lipoproteins, high density lipoproteins, or plasma proteins was also measured in each rabbit. The arterial influx was calculated as intimal clearance, i.e., the influx of a given fraction divided by its plasma concentration. The intimal clearance of low density lipoprotein esterified cholesterol was equal to that for the apolipoproteins of that fraction, which is compatible with an arterial influx of intact low density lipoprotein molecules. The intimal clearance of very low density apolipoprotein or cholesteryl ester was less than that for low density lipoprotein, whereas high density lipoprotein and albumin clearances exceeded low density lipoprotein clearance by 1.5- to 3-fold. The intimal clearances of plasma proteins, high density, low density, and very low density lipoproteins decreased linearly with the logarithm of the macromolecular diameter. This indicates that the arterial influx of three plasma lipoprotein fractions and of plasma proteins proceeds by similar mechanisms. Apparently the relative intimal clearances of lipoproteins are more dependent on their size relative to pores or vesicular diameters at the plasma-artery interface than on specific interactions between lipoproteins and the arterial intimal surface.