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 cardiomyocytes

The effects of schisandrin B stereoisomers, (±)γ-schisandrin [(±)γ-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 (Δψm) values, were examined in (±)γ-Sch-pretreated and (−)Sch B-pretreated cells, without or with hypoxia/reoxygenation challenge. The (±)γ-Sch and (−)Sch B (2.5–5.0 µM) pretreatments protected against hypoxia/reoxygenation-induced 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 µM in both (±)γ-Sch-pretreated and (−)Sch B-pretreated cells. The anti-apoptotic 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 (±)γ-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 (±)γ-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 Δψm in H9c2 cardiomyocytes, cytoprotection against hypoxia/reoxygenation-induced apoptosis afforded by (±)γ-Sch/(−)Sch B pretreatments was associated with a decreased sensitivity to Ca2+-induced MPT and an increased Δψm 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 MPT (r = − 0.615, P < 0.01) and positively with the values of Δψm (r = 0.703, P < 0.01) in (±)γ-Sch/(−)Sch B-pretreated and hypoxia/reoxygenation challenged cells. The results indicate that (±)γ-Sch/(−)Sch B pretreatment protected against hypoxia/reoxygenation-induced apoptosis in H9c2 cardiomyocytes and that the cytoprotection afforded by (±)γ-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.