Role of endogenous ceruloplasmin in low density lipoprotein oxidation by human U937 monocytic cells.

Abstract

Oxidation of lipids and lipoproteins by macrophages is an important event during atherogenesis. Activation of monocytic cells by zymosan and other agonists results in the release of multiple oxidant species and consequent oxidation of LDL. We now show evidence that ceruloplasmin, a copper-containing acute phase reactant, is secreted by zymosan-activated U937 monocytic cells, and that the protein has an important role in LDL oxidation by these cells. In one approach, ceruloplasmin has been shown to exhibit oxidant activity under the appropriate conditions. Exogenous addition of purified human ceruloplasmin stimulates U937 cell oxidation of LDL to nearly the same extent as activation by zymosan. In contrast to previous cell-free experiments (Ehrenwald, E., G. IntroductionActivated monocytes and macrophages are recognized for their remarkable diversity of secreted products, including multiple reactive oxygen and nitrogen intermediates, involved in the injury or killing of invasive organisms such as bacteria, parasites, and tumor cells (1). The same oxidation reactions may also cause secondary oxidative damage to host macromolecules and tissues during chronic inflammatory processes. For example, there is now abundant evidence that particles resembling oxidatively modified LDL are present in atherosclerotic lesions (2). Recent evidence suggests that oxidative damage is a critical factor in disease progression since antioxidants may reduce the onset or severity of cardiovascular disease (3) and inflammatory bowel diseases (4). The mechanisms of cellular oxidation processes have been subjected to intense scrutiny, but despite these efforts the physiological source(s) of transition metals required for metal ion-dependent oxidation reactions is not known (4, 5). A clue to the resolution of this enigma may be found in the observation by Cathcart et al. (6,7) that activated human monocytes, or monocytic cells such as the U937 cell line, oxidize LDL in vitro even in iron and copper ion-free media. This finding distinguishes these cells from endothelial cells and smooth muscle cells that require exogenous copper or iron salts in the medium to achieve optimal oxidation rates (8, 9). One explanation is that monocytic cells may provide their own transition metal ions to maintain high oxidation rates and the inhibition of monocytic cell lipid oxidation by divalent cation chelators is consistent with this idea (10). Alternatively, macrophage-derived hypochlorous acid or nitric oxide may be precursors of highly reactive hydroxyl radicals by metal ion-independent mechanisms (11).We have recently shown that physiological concentrations of purified human ceruloplasmin (200-400 g/ml in healthy adults) increase the oxidation of LDL in vitro by up to 50-fold when measured as thiobarbituric acid-reactive substances (TBARS) 1 (12). Ceruloplasmin is a monomeric, 132-kD acute

Ceruloplasmin gene expression in the murine central nervous system.

“…RNAse protection experiments using probes derived from the coding region of murine ceruloplasmin revealed that this larger transcript was not due to variations within the coding region (data not shown). Ceruloplasmin transcripts were detected in splenic reticuloendothelial cells concentrated in the marginal zones of the periarteriolar lymphoid sheets, consistent with data demonstrating ceruloplasmin gene expression in rat macrophages and human macrophage cell lines (39,40). In the spleen, these cells are responsible for the efflux of iron into the plasma after phagocytosis and digestion of senescent erythrocytes.…”

Identification of a Novel Family of Oxidized Phospholipids That Serve as Ligands for the Macrophage Scavenger Receptor CD36

“…Oxidation was terminated by addition of BHT (40 M) and DTPA (100 M) and dialysis against PBS containing DTPA (100 M). Oxidation of LDL by ceruloplasmin-bound copper was performed as described (33).…”

Plasma oxidative stress biomarkers and progesterone profiles in a dairy cow diagnosed with an ovarian follicular cyst

“…Ceruloplasmin is a serum ferroxidase that contains greater than 95% of the copper found in plasma (Hussein et al 2012) and is involved in cellular pro-oxidant and antioxidant processes (Ehrenwald & Fox 1996).…”