Abstract no.: 1
Statins and oxysterol‐induced vascular smooth muscle cell death

Abstract

Objective The strength of the fibrous cap of an atherosclerotic plaque is maintained by smooth muscle cells (SMCs). 7‐Ketocholesterol (7‐KC), and other oxysterols formed inside plaques, are known to induce SMC death, thereby increasing the risk of rupture and myocardial infarction (MI). Statins are known to protect patients from MI, but paradoxically they induce apoptosis in vascular SMCs as well. The aim of this study was to investigate the cell death effects of statins in 7‐KC‐treated SMCs. Methods Rabbit aorta SMCs (50 000; passage 2–6) were seeded in 24 well plates in HAM F10 with 10% foetal bovine serum (FBS). The next day, they were exposed to 25 μM 7‐KC and 10−8–10−4 M of fluvastatin (fluva), simvastatin (simva) or pravastatin (prava) in the presence of 2% FBS. Uptake of neutral red (0.01%, added 16 h later) was measured for 2 h as viability index. Results SMC viability decreased from 100% to 55 ± 3% (n = 28) upon 18 h exposure to 25 μM 7‐KC. High concentrations of fluva (≥ 10 μM) or simva (≥ 1 μM) also induced a concentration‐dependent loss of SMC viability; prava was always without effect. Interestingly, fluva and simva partly reversed the viability loss evoked by 7‐KC. Similar effects were seen when mitochondrial function was assessed using the succinate dehydrogenase substrate MTT. Fluva and simva alone were without effect, but they attenuated the mitochondrial dysfunction induced by 7‐KC. In contrast, both statins and 7‐KC enhanced the conversion of the caspase substrate DEVD‐R110 by SMC monolayers. Conclusions The results confirm that 7‐KC and high concentrations of lipophilic statins induce SMC death and activate caspases. Yet, in 7‐KC treated SMCs statins paradoxically attenuated viability loss and mitochondrial dysfunction. This clearly illustrates that drug effects seen in normal SMCs are not necessarily predictive of their action in an atherosclerotic setting.

Autophagy in atherosclerosis

“…Another example that illustrates the protective effects of autophagy in atherosclerosis comes from a recent pharmacologic study using statins and 7-ketocholesterol [35]. Statins protect patients from myocardial infarc- Model for the antiapoptotic effects of autophagy during oxidative injury in atherosclerosis.…”

“…SMC death induced by low concentrations of statins is not stimulated, but is attenuated, by the autophagy inducer 7-ketocholesterol. Indeed, fluvastatin fails to raise caspase activity in SMCs treated with 7-ketocholesterol, suggesting that the activation of autophagy interferes with the statin-induced apoptotic pathway [35]. The mechanisms of this suppression are not yet understood, but it has been proposed that the engulfment of defective mitochondria by autophagosomes limits the release of proapoptotic proteins, such as cytochrome C and apoptosis-inducing factor, into the cytosol [36].…”