TOXICITY OF OXYSTEROLS TO HUMAN MONOCYTE-MACROPHAGES

We have investigated the toxicity of the cholesterol oxidation product s (oxysterols), 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol, 7-ketocholesterol, 25-hydroxycholesterol and 26-hydroxycholesterol to human monocyte-macrophages in vitro. The 7-position derivatives are p resent in low density lipoprotein (LDL) oxidised with copper (II) sulp hate and by macrophages, and in extracts of human atherosclerotic lesi ons, which also contain 26-hydroxycholesterol. We have also assessed 2 5-hydroxycholesterol for toxicity because it has often been used in st udies of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitio n and LDL receptor down-regulation. Measurement of radioactivity relea se from monocyte-macrophages preloaded with tritiated adenine, as a me ans of assessing cytotoxicity, indicated that all the oxysterols showe d time- and concentration-dependent toxicity: The cytotoxic potency of 26-hydroxycholesterol was the greatest. The 7-position derivatives al so produced marked cell damage, though at higher concentrations than f or 26-hydroxycholesterol. Of the oxysterols assessed, the toxicity of 25-hydroxycholesterol was the least. The cytotoxicity of 7 beta-hydrox ycholesterol and 26-hydroxycholesterol was also shown using the 3-[4,5 -dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) dye redu ction assay which confirmed that 26-hydroxycholesterol was more toxic than 7 beta-hydroxycholesterol. Incubation of monocyte-macrophages wit h cholesterol added to the different oxysterols gave varying results. Cholesterol, which was not itself toxic, inhibited the toxicity of 25- hydroxycholesterol and 26-hydroxycholesterol, but the toxicity of the 7-position derivatives was not affected. The possible relevance of the se molecules to the death of macrophages seen in atherosclerosis is di scussed.