Apoptosis in Human Monocyte-Macrophages Exposed to Oxidized Low Density Lipoprotein

Abstract

This study has demonstrated the toxicity to human monocyte‐macrophages of low‐density lipoprotein (LDL) which had been artificially oxidized using copper sulphate. The assays of cell damage used were tritiated adenine release, neutral red staining, lactate dehydrogenase leakage, and MTT dye reduction. Toxicity was concentration‐ and time‐dependent. Exposure to native LDL under the same conditions did not result in toxicity. Transmission electron microscopy of cells exposed to oxidized LDL showed characteristic changes of apoptosis, including chromatin condensation and a decrease in cell volume. There was extensive loss of cell surface protrusions and evidence of the phagocytosis of apoptotic cells by neighbouring monocyte‐macrophages. Apoptotic features preceded the increased membrane permeability revealed by the release of radioactivity from cells preloaded with tritiated adenine and by lactate dehydrogenase leakage. DNA fragmentation was indicated by nick end‐labelling using the terminal transferase enzyme (TUNEL). The number of TUNEL‐positive cells was markedly greater in cells exposed to oxidized LDL, compared with those incubated as no‐additions controls. Inhibition of de novo protein synthesis with cycloheximide and of Ca2+/Mg2+‐activated endonuclease activity with aurintricarboxylic acid or zinc ion did not inhibit the toxicity produced by oxidized LDL.

Role of macrophage and smooth muscle cell apoptosis in association with oxidized low-density lipoprotein in the atherosclerotic development

“…OxLDL has a transient role in the mitogenic effect of macrophages, but finally causes cell death through the induction of apoptosis and necrosis. 31,32 Several factors such as ischemia, inflammatory cytokines, and the accumulation of toxic substances may also affect cell death in atherosclerotic plaques. 11 In this study, as for the relation of oxLDL to smooth muscle cell apoptosis, the apoptotic smooth muscle cell index increased with atherosclerotic development, and the apoptotic smooth muscle cells were detected mainly in the shoulder region and fibrous cap, where oxLDL-positive cells were predominant.…”

Peroxisome Proliferator-activated Receptor γ Agonists Inhibit HIV-1 Replication in Macrophages by Transcriptional and Post-transcriptional Effects

“…Plates were refed with DMEM (10% FBS) and incubated at 37°C with 5% CO 2 . MDM culture viability was assessed by reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) using a commercially available MTT assay kit (Roche Diagnostics Inc.) (31,32).…”

Oxidation-dependent effects of oxidized LDL: proliferation or cell death

“…Some of the functions were clearly contradictory with each other. OxLDL stimulated cell proliferation in smooth muscle cells (Auge et al, 1995;Auge et al, 1996;Chai et al, 1996) whereas it induced cell death in endothelial cells (Quinn, et al, 1985), smooth muscle cells (Nishio et al, 1996), or macrophages (Hardwick et al, 1996). However, it was difficult to explain why the oxLDL-induced cellular responses were contrary and which major contributor resulted in those responses.…”

“…Different investigators utilized different methods to oxidize LDL and present different criteria for LDL oxidation. For example, Bjorkerud and Bjorkerud (1996) and Auge, et al (1995) utilized UV-or Fe-mediated oxidation to prepare oxLDL while others used cell- (Quinn et al, 1985), enzyme- (Parhami et al, 1993) or copper- (Chai et al, 1996;Hardwick et al, 1996) mediated methods. They used different concentration and conditions of catalyst, and presented malondialdehyde (MDA) formation by thiobarbituric acid-reactive substances (TBARS) assay as a criterion for the oxidation extent.…”