Oxidation of Low-Density Lipoprotein by Human Monocyte-Macrophages Results in Toxicity to the Oxidising Culture

Abstract

Human monocyte-macrophage cultures were exposed to native low density lipoprotein (LDL) for up to 24 h in Ham's F10 medium and the extent of cell-mediated LDL oxidation was determined by measurement of electrophoretic mobility on agarose gels and measurement of lipids and oxidised lipids (including 7 beta-hydroxycholesterol) by GC. After an initial lag phase, which varied from 2-8 h, there was a steady increase in oxidation over 24 h. No-cell control incubations showed minimal increases in oxidation over 24 h. Significant toxicity, measured as release of radioactivity from macrophages pre-loaded with tritiated adenine, was observed in the cells when they oxidised LDL and the extent of radioactivity release correlated closely with the extent of LDL oxidation. Inhibition of oxidation using alpha-tocopherol or probucol reduced toxicity within the oxidising culture. This self-inflicted toxicity may help to explain the origin and enlargement of the lipid core of advanced atherosclerotic lesions.

Inhibition of lipoprotein‐associated phospholipase A2 diminishes the death‐inducing effects of oxidised LDL on human monocyte‐macrophages

“…The isolation of human monocytes from blood (normal volunteers) or buffy coat (National Blood Service), HMM culture (in Macrophage‐SFM serum‐free medium), LDL preparation, HMM‐mediated LDL oxidation (in Ham's F‐10 medium supplemented with 3 μM Fe 2 SO 4 , 10.8 mg/l phenol red and 2 mM glutamine), measurement of relative electrophoretic mobility (REM) and of thiobarbituric acid‐reactive substances (TBARS) was as described previously [1,3,25,26]. Measurement by gas chromatography (GC) of free plus esterified individual fatty acids and 7β‐hydroxycholesterol (7β‐HC) in LDL and oxLDL was as before [3].…”

Modified Low Density Lipoprotein and Lipoprotein-Containing Circulating Immune Complexes as Diagnostic and Prognostic Biomarkers of Atherosclerosis and Type 1 Diabetes Macrovascular Disease

“…The accumulation of foam cells in the arterial wall causes formation of initial lesion and then fatty streaks that actually represent early lesions in proatherogenic progression [86]. In addition, intracellular accumulation of modified LDL is cytotoxic for resident cells and macrophages and hence initiates inflammatory response against apoptotic and necrotic cells [87,88]. …”

Inhibition of in vitro macrophage-induced low density lipoprotein oxidation by thyroid compounds

“…Indeed, as reported by others, we have checked in preliminary studies that (1) very little if any macrophage LDL oxidation occurred in RPMI-1640 supplemented with up to 10 µM Fe 2+ (Müller et al 1998, Van Reyk et al 1999, (2) iron was necessary to catalyze macrophage-mediated LDL oxidation (Müller et al 1998, Yuan & Brunk 1998, and (3) Ham's F-10 medium containing 3 µM Fe 2+ ought to be supplemented with an additional 5 µM Fe 2+ in order to avoid limitation of LDL oxidation which may occur in some LDL preparations (Marchant et al 1996). Note that this Fe 2+ concentration induced neither LDL peroxidation in the absence of cells (Fig.…”

“…As a result, the rather significant inhibition of LDL lipid peroxidation by TA 3 (Fig. 3) may be explained, at least in part, by (1) a partial destruction of cells which reduce their pro-oxidant capabilities (Marchant et al 1996, Müller et al 1998, and (2) an artefact due to the calculation of this inhibition, i.e. subtraction of TBARS due to cell lipid peroxidation from those due to cell and LDL lipid peroxidation.…”