Navel effects of the acyl-coenzyme A : cholesterol acyltransferase inhibitor 58-035 on foam cell development in primary human monocyte-derived macrophages

We examined the effect of acyl-coenzyme A:cholesterol acyltransferase (ACAT ) inhibitors on intracellular cholesterol, stores in primary human monocyte -derived macrophages (HMs) during foam cell formation. HMMs were exposed to acetylated low density lipoprotein (acLDL, 500 mu g protein per mt) with o r without 58-035 (1 to 10 mu g/mL) or Cl-976 (2 mu g/mL) for 2 to 48 hours. Total cholesterol (TC) and esterified cholesterol (EC) mass was significan tly lower while unesterified cholesterol (UC) increased slightly in cells i ncubated with acLDL plus ACAT inhibitors. Sterol mass was also measured in cells coincubated with acLDL (500 mu g protein per mt) with or without 58-0 35 (2 mu g/mL), high density lipoprotein (HDL, 400 mu g protein per mt), or HDL + 58-035 for 48 hours. TC and EC were 23% and 55% lower, respectively (P<0.0004), while UC was 11% higher (P<0.04) in cells incubated with acLDL plus 58-035. In contrast, coincubation with HDL alone did not significantly affect TC, EC, or UC mass compared with acLDL alone. The effect of 58-035 could not be explained by cytotoxicity, because adenine release, secreted l actate dehydrogenase, glucose utilization, and cell protein were similar in cells exposed to acLDL regardless of the presence of 58-035. We investigat ed several potential mechanisms for the decreased TC mass, including increa sed UC efflux and decreased acLDL binding and uptake. Efflux was measured i n cells exposed to [1,2-H-3]cholesteryl oleate-labeled acLDL, unlabeled con trol acLDL, and native untreated acLDL (500 mu g protein per mt) with or wi thout 58-035 (5 mu g/mL) for 24 or 48 hours. UC efflux increased in a time- dependent manner from cells exposed to acLDL plus 58-035 compared with cell s exposed to acLDL alone (P<0.04). High-affinity binding was measured in ce lls exposed to I-125-acLDL (5 mu g protein per mt) with or without excess u nlabeled acLDL (100 or 500 mu g protein per mt) for 4 hours at 4 degrees C. Specific acLDL binding, uptake, and total degradation were significantly l ower when 58-035 was present during cholesterol enrichment compared with ce lls exposed to acLDL alone (P<0,001). Unlike the effects of ACAT inhibitors on foam cell formation in rodent macrophages, these compounds lowered TC a ccumulation in HMMs during foam cell formation by limiting the uptake of ac LDL and enhancing UC efflux. They may offer promise as drug therapies for a therosclerosis.