Schisandrin B stereoisomers protect against hypoxia/reoxygenation-induced apoptosis and associated changes in the Ca²⁺-induced mitochondrial permeability transition and mitochondrial membrane potential in AML12 hepatocytes

The effects of the schisandrin B stereoisomers, (±)γ-schisandrin [(±)γ-Sch] and (-)schisandrin B [(-)Sch B], on hypoxia/reoxygenation-induced apoptosis were investigated in AML12 hepatocytes. Changes in cellular reduced glutathione (GSH) levels, Ca²⁺-induced mitochondrial permeability transitions (MPTs) and mitochondrial membrane potentials (Δψm values) were also examined in (±)γ-Sch- and (-)Sch B-treated cells, without or with hypoxia/reoxygenation challenge. The (±)γ-Sch/(-)Sch B pretreatments (2.5-5.0 μm) protected against hypoxia/reoxygenation-induced apoptosis in AML12 cells in a concentration-dependent manner, with the (-)Sch B effect being more potent. Drug antiapoptotic effects were further evidenced by suppression of hypoxia/reoxygenation-induced mitochondrial cytochrome c release and subsequent cleavage of caspase 3 and poly-ADP-ribose polymerase by (-)Sch B pretreatment. Whereas hypoxia/reoxygenation challenge increased the extent of Ca²⁺-induced MPT pore opening, and Δψm, in AML12 hepatocytes, cytoprotection afforded by (±)γ-Sch/(-)Sch B pretreatment against hypoxia/reoxygenation-induced apoptosis was associated with a decreased sensitivity to Ca²⁺-induced MPT and an increased Δψm in both unchallenged and challenged cells, compared with the drug-free control. The results indicate that (±)γ-Sch/(-)Sch B pretreatment protected against hypoxia/reoxygenation-induced apoptosis in AML12 hepatocytes and that the cytoprotection afforded by (±)γ-Sch/(-)Sch B may at least in part be mediated by a decrease in sensitivity to Ca²⁺-induced MPT, which may in turn result from enhancement of cellular GSH levels by drug pretreatments. Copyright © 2009 John Wiley & Sons, Ltd.