7‐ketocholesterol and 5,6‐secosterol modulate differently the stress‐activated mitogen‐activated protein kinases (MAPKs) in liver cells

Abstract

Enhanced oxidative stress is a common feature of liver diseases and contributes to chronic liver disease (CLD) progression by inducing fibrogenesis during liver regeneration. Peroxidation products of cholesterol metabolism, named oxysterols, are new and reliable markers of oxidative stress in vivo. Patients affected by CLDs present high plasma levels of oxysterols, raising the question of the origin and biological relevance of these compounds in the pathophysiology of chronic liver damage. The aim of this study was to examine the molecular basis of the biological effects of oxysterols on liver-derived cells, HepG2 and Huh7. Cells were treated with different concentrations (10(-9) to 10(-5) M) of 7-ketocholesterol used as a reference, and 5,6-secosterol, a recently discovered oxysterol. FACS investigations, caspase-3 activation, and Sytox Green immunofluorescent assay showed that pathological concentrations of oxysterols induced necrosis (30-50%) after 48 h of treatment. The two analyzed compounds displayed a similar, but not identical, behavior. In fact, 5,6-secosterol, but not 7-ketocholesterol, induced cell senescence. Notably, low concentrations of 5,6-secosterol caused a sustained activation of ERK1/2, inducing cell proliferation, this unexpected behavior should be better characterized by further studies. Since enhanced oxidative stress is known to worsen liver chronic hepatitis and frequently results in overall decreased cellular survival, our data suggest the important and different role oxysterols may have in interfering with physiological liver tissue regeneration in injured human liver. Antioxidant treatment may provide a highly specific and effective mean to counteract the common consequences of oxidative stress on chronic hepatitis, such as fibrosis/cirrhosis and liver failure.

Mechanisms of oxysterol-induced carcinogenesis

“…22R-hydroxycholesterol stabilizes COX-2 mRNA via the 38-MAPK pathway in human cholangiocytes [51]. Hepatocellular carcinoma cells HepG2 and Huh7 senesce via alteration of p38 MAPK when treated with 5,6 secosterol [81]. Moreover, bile acids, which can be considered a type of oxysterol in bile, are known to activate various signaling cascades.…”

Cytotoxic Effects of Secosterols and Their Derivatives on Several Cultured Cells

“…13) Moreover, several pathways have been postulated for secosterol-triggered cell death, including the caspase-3/ 7-dependent pathway and the mitochondrial and death receptor pathway in cardiomyocyte H9c2 cells, 14,15) the reactive oxygen species-dependent pathway in hypothalamic neuron GT1-7 cells, 13,16) a mitochondrial death pathway in macrophage J774 cells, and the mitogenactivated protein kinase pathway in hepatocarcinoma HepG2 and Huh7 cells. 17) As noted above, we found recently that synthesized secosterol-A added to a culture medium containing 10% FBS was very unstable and was rapidly (within 10 s) converted to secosterol-B and the aldehyde-oxidation product of secosterol-A, 3-hydroxy-5-oxo-secocholestan-6-oic acid (secoA-COOH), the yields being 81.4 and 10.6%, respectively. 4) Moreover, about 20% of secosterol-B was further converted to its aldehyde-oxidation product, 3-hydroxy-5-hydroxy-B-norcholestane-6-oic acid (secoB-COOH).…”

Oxysterols and Their Cellular Effectors

“…The kinases implicated in apoptosis belong to mitogen activated protein kinase (MAPK), Akt/PKB, and the protein kinase C families (reviewed by Lordan et al , [11]). Anticoli et al [98] reported that 7-KC and 5,6-secosterol modulate differently the stress-activated MAPKs in liver cells: Pathologic concentrations of both oxysterols induced necrosis of the cells after 48 h treatment. 5,6-secosterol, but not 7-KC, induced cell senescence at high concentrations, but caused sustained ERK1/2 (extracellular signal activated kinases) activation and cellular proliferation at low concentrations.…”