Bryophyllum pinnatum modulation of signaling pathways relevant for preterm labor in human myometrial cells

Preparations of Bryophyllum pinnatum have been used as a well-tolerated treatment of preterm labor, initially in anthroposophic hospitals and, more recently, also in conventional settings. In vitro studies with human myometrial cells have shown that B. pinnatum leaf press juice inhibits both intracellular Ca^{2 +} signaling and the activation of inflammatory pathways induced by the relevant hormone oxytocin. However, the compounds responsible for these inhibitory effects and the potential involvement of related signaling pathways remain unknown. In the present study, we aim to address these knowledge gaps. In vitro experiments were conducted in hTERT-C3 human myometrial cells, using alamarBlue assay, fluorescent intracellular Ca²⁺ assay, ELISA, proteomics and real-time PCR. Contractility studies were conducted in an ex vivo organ bath model using human myometrial tissue. No single compound from B. pinnatum leaves mimicked the inhibitory effect of the whole leaf press juice on OT-induced Ca²⁺ signaling. However, a bufadienolide-enriched fraction and the bufadienolides bersaldegenin-1,3,5-acetate, bryophyllin A and bersaldegenin-3-acetate, but not bersaldegenin-1-acetate, reduced OT-induced COX-2 expression and attenuated NFκB activation. That the juice can inhibit prostaglandin F_2α-induced contractions was shown in the myometrium bath model. Proteomics analysis revealed that the leaf juice reduced expression of various extracellular matrix proteins. Cell viability assays showed that the various inhibitory effects cannot be attributed to cytotoxicity. Taken together, these results further support investigations on the use of B. pinnatum as a well-tolerated candidate for long-term treatment of preterm labor.