Diabetic Hyperglycaemia Protects Smooth Muscle Arterial Cells but Not Macrophages and Endothelial Cells from the Cytotoxic Effects of 7-Ketocholesterol: An In Vitro Study

ABSTRACT Plasmatic hyperglycaemia is responsible for positive and negative stimuli. Among responsive cells, smooth muscle cells respond actively, increasing their growth. Diabetes hyperglycaemia and lipidic disorders are frequently associated, resulting in the highest probability of cardiovascular disease, especially atherosclerosis. Endothelial dysfunction and initiation of inflammatory process mediated by macrophages cause the formation of atherosclerotic plaques, rich in oxidized cholesterol, mostly 7-ketocholesterol. In this study, we evaluated the effect of 7-ketocholesterol in rabbit aorta endothelial cells, murine macrophages (J774) and smooth muscle cells (A7R5) maintained in normoglycemic and hyperglycaemic cultures. The 7-ketocholesterol-induced-cell death was observed in the normoglycemic medium three times more than the hyperglycaemic medium in all cells. High glucose medium had a protective effect on arterial smooth muscle cell death.

Effect of Extracellular Signal-Regulated Kinase Inhibition on Oxysterol 7-Ketocholesterol-Induced Apoptosis

BACKGROUND: Defects in mitochondrial function have been shown to participate in the induction of neuronal cell injury. The extracellular-signal-regulated kinase (ERK) signaling pathway plays a crucial role in almost all cell functions, including proliferation, differentiation, survival, and death. However, the effect of ERK inhibition on oxysterol-induced apoptosis remains uncertain. METHODS: This study assessed the effect of ERK inhibition on the apoptotic effect of 7-ketocholesterol. RESULTS: Treatment with 7-ketocholesterol increased phosphorylated-ERK1/2 levels in differentiated PC12 cells, while the total amount of ERK was not altered. 7-Ketocholesterol decreased Bid and Bcl-2 levels, increased Bax and p53 levels, and promoted cytochrome c release, which elicits the activation of caspases (-8, -9, and -3), nuclear damage, and cell death. ERK and farnesyltransferase inhibitors inhibited the 7-ketocholesterol-induced phosphorylation of ERK1/2, activation of apoptosis-related proteins, and cell death in PC12 cells. CONCLUSIONS: The ERK and farnesyltransferase inhibitors, which did not exhibit toxicity, may inhibit the 7-ketocholesterol toxicity on differentiated PC12 cells by suppressing the activation of the caspase-8-dependent pathway as well as activation of the mitochondria-mediated cell-death pathway, leading to the activation of caspases. The inhibition of ERK may confer a beneficial protective effect against the neuronal cell injury induced by cholesterol oxidation products.

Synthetic nanoemulsion resembling a protein-free model of 7-ketocholesterol containing low density lipoprotein: In vitro and in vivo studies

7-ketocholesterol (7-KC) differs from cholesterol by a functional ketone group at C7. It is an oxygenated cholesterol derivative (oxysterol), commonly present in oxidized low-density lipoprotein (LDL). Oxysterols are generated and participate in several physiologic and pathophysiologic processes. For instance, the cytotoxic effects of oxidized LDL have been widely attributed to bioactive compounds like oxysterols. The toxicity is in part due to 7-KC. Here we aimed to demonstrate the possibility of incorporating 7-KC into the synthetic nanoemulsion LDE, which resembles LDL in composition and behavior. This would provide a suitable artificial particle resembling LDL to study 7-KC metabolism. We were able to incorpórate 7-KC in several amounts into LDE. The incorporation was evaluated and confirmed by several methods, including gel filtration chromatography, using radiolabeled lipids. The incorporation did not change the main lipid composition characteristics of the new nanoparticle. Particle sizes were also evaluated and did not differ from LDE. In vivo studies were performed by injecting the nanoemulsion into mice. The plasma kinetics and the targeted organs were the same as described for LDE. Therefore, 7-KC-LDE maintains composition, size and some functional characteristics of LDE and could be used in experiments dealing with 7-ketocholesterol metabolism in lipoproteins.

Prostaglandin E2 Attenuates 7-Ketocholesterol Toxicity by Suppressing Changes in Mitochondria-Associated Cell Death Process

BACKGROUND: It has been shown that defects in mitochondrial function are involved in the induction of neuronal cell injury. Prostanoids such as prostaglandin E2 (PGE2) are thought to play an important role in inflammation and neurologic disorders. However, the effect of PGE2 on cholesterol-oxidation-product-induced neuronal cell injury remains uncertain. METHODS: The effect of PGE2 on toxicity of 7-ketocholesterol (7-KCS) was assessed in PC12 cells that were differentiated following treatment with nerve growth factor. The mitochondria-mediated apoptotic process was evaluated by examining the inhibitory effect of PGE2 on 7-KCS-induced toxicity. RESULTS: 7-KCS induced BID cleavage, increased the production of proapoptotic Bax protein, decreased antiapoptotic Bcl-2, increased p53, and promoted cytochrome c release in the cytosolic fraction, which subsequently elicited the activation of caspase-3, DNA fragmentation, and cell death. Treatment with PGE2 inhibited this 7-KCS-induced apoptotic process and cell death. CONCLUSIONS: The results show that PGE2 inhibits 7-KCS-induced toxicity in differentiated PC12 cells by suppressing the mitochondria-mediated apoptotic process. PGE2 may protect against cholesterol-oxidation-product-induced neuronal cell injury.

Cytoprotective effect of polysaccharide isolated from different mushrooms against 7-ketocholesterol induced damage in mouse liver cell line (BNL CL. 2)

Cytoprotective ability of polysaccharides isolated from different edible mushrooms was investigated on the 7-ketocholesterol-induced damaged cell line. Polysaccharide extracts from six different edible mushrooms-Flammulina velutipes, Peurotus ostreatus, Lentinus edodes, Agrocybe aegerita, Agaricus blazei, and Cordyceps militaris- were prepared by hot water extraction and alcohol precipitation. Cytoprotective ability was evaluated by measuring the viable cells of the normal embryonic liver cell line (BNL CL. 2) in the presence of 7-ketocholesterol. At 80 microgram/mL of 7-ketocholesterol, cytotoxicity was very high with a loss of 98% of viable cells after 20 h of incubation. With the addition of 200 microgram/mL of each polysaccharide isolate to the cell line containing 80 microgram/mL of 7-ketocholesterol, polysaccharide isolates from both Flammulina velutipes and Peurotus ostreatus could significantly inhibit the 7-ketochoelsterol-induced cytotoxicity in the cells. But other polysaccharide isolates were not effective in inhibiting cell damage caused by the oxLDL-induced cytotoxicity.