Schisandrin B stereoisomers protect against hypoxia/reoxygenation-induced apoptosis and inhibit associated changes in Ca2+-induced mitochondrial permeability transition and mitochondrial membrane potential in H9c2 cardiornyocytes

The effects of schisandrin B stereoisomers, (+/-)gamma-schisandrin [(+/-)gamma-Sch] and (-)schisandrin B [(-)Sch B], on hypoxia/reoxygenation-induced apoptosis were investigated in H9c2 cardiomyocytes. Changes in cellular reduced glutathione (GSH) levels, Ca2+-induced mitochondrial permeability transition (MPT), and mitochondrial membrane potential (Delta psi(m)) values, were examined in (+/-)gamma-Sch-pretreated and (-)Sch B-pretreated cells, without or with hypoxia/reoxygenation challenge. The (+/-)gamma-Sch and (-)Sch B (2.5-5.0 mu M) pretreatments protected against hypoxia/reoxygenation-incluced apoptosis of H9c2 cells in a concentration-dependent manner, with (-)Sch B being more potent. The degrees of protection decreased, however, at the higher drug concentrations of 7.5 mu M in both (+/-)gamma-Sch-pretreated and (-)Sch B-pretreated cells. The antiapoptotic effects of the drugs were further evidenced by the suppression of hypoxia/reoxygenation-induced mitochondrial cytochrome c release and the subsequent cleavage of caspase 3 and poly-ADP-ribose polymerase after (-)Sch B pretreatment. Both (+/-)gamma-Sch and (-)Sch B pretreatments increased GSH levels in H9c2 cells, with (-)Sch B being more potent. Hypoxia/reoxygenation challenge caused a depletion in cellular GSH and the cytoprotection afforded by (+/-)gamma-Sch/(-)Sch B was associated with enhancement of cellular GSH in H9c2 cells, as compared to the drug-unpretreated control. Whereas hypoxia/reoxygenation challenge increased the extent of Ca2+-induced MPT pore opening and decreased Delta psi(m) in H9c2 cardiornyocytes, cytoprotection against hypoxia/reoxygenation-incluced apoptosis afforded by (+/-)gamma-Sch/(-)Sch B pretreatments was associated with a decreased sensitivity to Ca2+-induced MPT and an increased Delta psi(m), in both unchallenged and challenged cells, as compared to the respective drug-unpretreated controls. The degrees of protection against apoptosis correlated negatively with the extents of Ca2+-induced MIPT (r=-0.615, P < 0.01) and positively with the values of Delta psi(m) (r=0.703, P < 0.01) in (+/-)gamma-Sch/(-)Sch B-pretreated and hypoxia/ reoxygenation challenged cells. The results indicate that (+/-)gamma-Sch/(-)Sch B pretreatment protected against hypoxia/reoxygenation-induced apoptosis in H9c2 cardiornyocytes and that the cytoprotection afforded by (+/-)gamma-Sch/(-)Sch B may at least in part be mediated by a decrease in cellular sensitivity to Ca2+-induced MPT, which may in turn result from enhancement of cellular GSH levels by drug pretreatments. (c) 2008 Elsevier Inc. All rights reserved.