Oxidised low-density lipoprotein (OXLDL) causes calcium influx and activates mitochondrial permeability transition (MPT) in human macrophages

Abstract

Oxidized low-density lipoprotein (oxLDL) plays an important role in atherosclerosis development. Studies have implicated the involvement of macrophages and the presence of oxLDL in atherosclerotic plaque. OxLDL is cytotoxic to human macrophages, causing a rapid and concentration and time-dependent cell death. This study aimed to investigate the mechanism of cell death induced by oxLDL in human macrophages. Human macrophages were treated with different concentrations of tetramethylrhodamine methyl ester (TMRM), ruthenium red (RuR) or cyclosporin A (CsA) for 30 minutes followed by addition of median lethal concentration (LC50) of oxLDL and were incubated at 37oC. Fluorescence levels were measured using flow cytometry for TMRM and dihydroethidium (DHE) after a designated incubation time. Cell viability was determined using propidium iodide (PI) via flow cytometry after 24 hours. TMRM results showed that oxLDL caused a time-dependent mitochondrial membrane potential (∆Ψm) loss. Cells treated with RuR and CsA were protected from oxLDL toxicity, possibly by reducing reactive oxygen species (ROS) production and preventing MPT pores opening, respectively. Our findings showed that blocking calcium uptake into the mitochondria may reduce ROS generation and prevents MPT activation. This indicates that oxLDL insult to the mitochondria might play a vital role in oxLDL-induced cell death.