title: Silymarin prevents palmitate-induced lipotoxicity in HepG2 cells: involvement of maintenance of Akt kinase activation.
abstract: Whereas adipocytes have a unique capacity to store excess free fatty acids in the form of triglyceride in lipid droplets, non-adipose tissues, such as liver, have a limited capacity for storage of lipids. Saturated long-chain fatty acids, such as palmitate, are the major contributors to lipotoxicity. Silymarin is a mixture of flavonolignans, extracted from the milk thistle (Silibum marianum). Its hepatoprotective properties have been studied both in vitro and in vivo; however, its effect on palmitate-induced lipotoxicity has not been investigated. The objective of this study was to investigate (i) whether silymarin could protect HepG2 cells from palmitate-induced cell death in an in vitro model, and (ii) possible mechanisms involved in this hepatoprotective role of silymarin. HepG2 cells were treated with palmitate in the absence or presence of silymarin and supernatants or cell lysates were collected at varying time-points. Cell death was assayed by measuring DNA fragmentation, caspase-3 activity and lactate dehydrogenase release. Lipid peroxidation was assessed by measuring malondialdehyde and 4-hydroxyalkenals. Akt kinase activity was also measured. Incubation with palmitate caused significant death in HepG2 cells. Palmitate incubation did not cause significant changes in reactive oxygen species production or intracellular glutathione content, but markedly inhibited Akt kinase activity. Pre-treatment of HepG2 cells with silymarin prevented palmitate-induced inhibition of Akt kinase activity and attenuated cell death. Our results suggest that silymarin may be an effective agent in protecting hepatocytes from saturated fatty acids-induced cell death. These data also provide a further rationale for exploration of the use of silymarin in the treatment of non-alcoholic steatohepatitis.
authors.affiliation: Division of Gastroenterology/Hepatology, Department of Internal Medicine, University of Louisville School of Medicine, 511 S. Floyd Street, Louisville, KY 40202, USA. z0song02@louisville.edu
authors.forename: Zhenyuan
authors.initials: Z
authors.lastname: Song
authors.forename: Ming
authors.initials: M
authors.lastname: Song
authors.forename: David Y W
authors.initials: DY
authors.lastname: Lee
authors.forename: Yanze
authors.initials: Y
authors.lastname: Liu
authors.forename: Ion V
authors.initials: IV
authors.lastname: Deaciuc
authors.forename: Craig J
authors.initials: CJ
authors.lastname: McClain
mesh_terms: D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D053938:DNA Fragmentation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D020944:Silybum marianum; D010168:Palmitates / Q000633:toxicity*; D020011:Protective Agents / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012838:Silymarin / Q000494:pharmacology*
chemical_list: D010168:Palmitates; D020011:Protective Agents; D017382:Reactive Oxygen Species; D012838:Silymarin; D007770:L-Lactate Dehydrogenase; D051057:Proto-Oncogene Proteins c-akt; D053148:Caspase 3