Bryophyllum pinnatum has been used in the treatment of premature labor, first in anthroposophic hospitals and, recently, in conventional settings as an add-on medication. In vitro work with hTERT human myometrial cells showed that B. pinnatum leaf press juice inhibits the increase of intracellular free calcium concentration induced by oxytocin, a hormone known to play a role in labor. Our aim was to identify fractions/compounds in B. pinnatum press juice that contribute to this inhibitory effect, and to investigate their effect on oxytocin-driven activation of the MAPK cascade. Several fractions/compounds from B. pinnatum press juice led to a concentration-dependent decrease of oxytocin-induced increase of intracellular free calcium concentration, but none of them was as strong as B. pinnatum press juice. However, the combination of a bufadienolide and a flavonoid-enriched fraction was as effective as B. pinnatum press juice, and their combination had a synergistic effect. B. pinnatum press juice inhibited oxytocin-driven activation of MAPKs SAPK/JNK and ERK1/2, an effect also exerted by the bufadienolide-enriched fraction. The effect of B. pinnatum press juice on oxytocin-induced signaling pathways was comparable to that of the oxytocin-receptor antagonist and tocolytic agent atosiban. Our findings further substantiate the use of B. pinnatum press juice preparations in the treatment of preterm labor.

In the published article, there was an error for the units used to report the press juice concentration. The units were incorrectly written as µg/mL, instead of mg/mL. In the original article, this error appeared in the legend for Figure 4, in Figures 1-3 and in the Materials and Methods and Results sections.A correction has been made to Materials and Methods, Phosphorylation Experiments, Paragraph number 1. This sentence previously stated:"hTERT-C3 cells (4.7 × 10 4 cell/mL) were seeded into 6-well plates three to 4 days before experiments were performed. Once 90% confluence was reached, cells were treated with OT (100 nM) for 2, 5, 15, 30 or 45 min. To investigate the modulation of OT-induced phosphorylation under these conditions, cells were pre-treated with BPJ (2% corresponding to 20 μg/mL), atosiban (100 nM) or just medium. In additional experiments, cells were pretreated with BPJ (20 μg/mL), BEF (2.20 μg/mL), FEF (17.39 μg/mL), A-Mix (0.68 μg/mL), BEF plus FEF and BEF plus A-Mix (same concentrations as in the single treatments), or just medium for 30 min before stimulation with OT for 5 min."The corrected sentence appears below: "hTERT-C3 cells (4.7 × 10 4 cell/mL) were seeded into 6-well plates three to 4 days before experiments were performed. Once 90% confluence was reached, cells were treated with OT (100 nM) for 2, 5, 15, 30 or 45 min. To investigate the modulation of OT-induced phosphorylation under these conditions, cells were pre-treated with BPJ (2% corresponding to 20 mg/mL), atosiban (100 nM) or just medium. In additional experiments, cells were pretreated with BPJ (20 mg/mL), BEF (2.20 μg/mL), FEF (17.39 μg/mL), A-Mix (0.68 μg/mL), BEF