Cholesterol Crystals Activate the NLRP3 Inflammasome in Human Macrophages: A Novel Link between Cholesterol Metabolism and Inflammation

Chronic inflammation of the arterial wall is a key element in the pathogenesis of atherosclerosis, yet the factors that trigger and sustain the inflammation remain elusive. Inflammasomes are cytoplasmic caspase-1-activating protein complexes that promote maturation and secretion of the proinflammatory cytokines interleukin(IL)-1beta and IL-18. The most intensively studied inflammasome, NLRP3 inflammasome, is activated by diverse substances, including crystalline and particulate materials. As cholesterol crystals are abundant in atherosclerotic lesions, and IL-1beta has been linked to atherogenesis, we explored the possibility that cholesterol crystals promote inflammation by activating the inflammasome pathway.Here we show that human macrophages avidly phagocytose cholesterol crystals and store the ingested cholesterol as cholesteryl esters. Importantly, cholesterol crystals induced dose-dependent secretion of mature IL-1beta from human monocytes and macrophages. The cholesterol crystal-induced secretion of IL-1beta was caspase-1-dependent, suggesting the involvement of an inflammasome-mediated pathway. Silencing of the NLRP3 receptor, the crucial component in NLRP3 inflammasome, completely abolished crystal-induced IL-1beta secretion, thus identifying NLRP3 inflammasome as the cholesterol crystal-responsive element in macrophages. The crystals were shown to induce leakage of the lysosomal protease cathepsin B into the cytoplasm and inhibition of this enzyme reduced cholesterol crystal-induced IL-1beta secretion, suggesting that NLRP3 inflammasome activation occurred via lysosomal destabilization.The cholesterol crystal-induced inflammasome activation in macrophages may represent an important link between cholesterol metabolism and inflammation in atherosclerotic lesions

Inhibition of Acyl-CoA: Cholesterol acyltransferase (ACAT), overexpression of cholesterol transporter gene, and protection of amyloid β (Aβ) oligomers-induced neuronal cell death by tricyclic pyrone molecules

Alzheimer’s disease (AD) is the most common cause of dementia in the elderly. A major effort in AD therapeutic development has targeted Aβ and downstream events. We have taken a rational design approach and synthesized a small library of tricyclic pyrone compounds based on CP2. Their protective action in MC65 cells and the inhibition of acyl‐CoA:cholesterol acyltransferase along with the upregulation of cholesterol transporter gene were investigated. Five most active compounds exhibited potencies in the nanomolar to low micromolar ranges. The multiple effects of the compounds on Aβ and cellular cholesterol pathways could be potential mechanisms underlying the protective effects in vivo

Statin therapy alone and in combination with an acyl-CoA:cholesterol O-acyltransferase inhibitor on experimental atherosclerosis

The ability to modify the enzymatic processes involved in promoting atherosclerotic plaque disruption and to serially monitor atherosclerotic evolution could provide novel information in the management of patients with atherosclerosis. We studied the effects of a statin (atorvastatin) and its combination with an acyl-CoA:cholesterol O-acyltransferase (ACAT) inhibitor (avasimibe) on atherosclerotic regression and plaque stability as measured by matrix metalloproteinase 1 and 3 (MMP-1 and MMP-3) levels. Watanabe Heritable Hyperlipidemic (WHHL) rabbits treated with atorvastatin alone experienced an attenuated increase in atherosclerotic burden versus controls as determined by MR imaging. The mean vessel wall area (VWA) prior to drug therapy was 5.57 ± 0.01 mm2. The VWA increased to 6.71 ± 0.03 and 7.16 ± 0.03 mm2, respectively, in atorvastatin-treated and control groups (p < 0.0001 for both). The combination of atorvastatin and avasimibe induced a significant regression of the previously established atherosclerotic lesions, with the VWA decreasing to 4.54 ± 0.04 mm2 (p = 0.009). Atorvastatin alone induced a nonsignificant reduction in the percent staining of MMP-1 in atherosclerotic lesions, but the combination treatment with avasimibe led to a significant reduction versus controls (p = 0.005). However, a reduction in MMP-3 staining was significant for rabbits treated with both atorvastatin alone (p = 0.007) and in combination with avasimibe (p = 0.04) versus controls. In this animal model, the addition of avasimibe to atorvastatin has beneficial effects on both atherosclerotic plaque regression and stabilization