Pharmaceutical research on Bryophyllum pinnatum – in vitro effects on human myometrial contractility

Bryophyllum pinnatum is a succulent perennial plant used in the treatment of premature labour, first in anthroposophic medicine and, recently in many perinatal clinics in Switzerland, as a monotherapy or add-on therapy with known tocolytic agents. The good effectiveness, as well as the very good tolerability, have been confirmed by several studies. Earlier experimental evidence obtained from in vitro studies supports its use. Preterm birth is the number one cause of newborn mortality and morbidity, and often results from preterm labour. Since preterm uterine contractions are frequently associated with preterm birth, their inhibition by tocolytics may delay delivery long enough (24-48 h) to achieve foetal lung maturation. Currently used tocolytics include oxytocin (OT) receptor antagonists (e.g. atosiban), calcium channel blockers (e.g. nifedipine) and β-sympathomimetics, among others. Due to tocolytics’ side effects and insufficient therapeutic effects, additional therapeutic options are needed. For the administration of a phytotherapeutic, it is necessary to have knowledge not only about their therapeutic effect and toxicity, but also about their mode of action. This thesis describes the effects of B. pinnatum on human myometrium contractility.
Because a combination of different drugs might prove to be helpful in achieving a prolongation of pregnancy in more patients, B. pinnatum in combination with the two tocolytics was tested in vitro. Myometrium strips placed under tension in an organ bath were allowed to contract spontaneously. The addition of B. pinnatum press juice (BPJ), atosiban, and nifedipine moderately reduced the strength (area under the curve (AUC) and amplitude) of contractions. When BPJ was added together with atosiban or nifedipine, the reduction of contraction strength was significantly higher than with the tocolytics alone. The inhibitory effects of BPJ plus atosiban and of BPJ plus nifedipine on contractions strength were concentration-dependent and, none of the substances, alone or in combination, decreased myometrial cell viability.
A previous metabolite profile study of B. pinnatum leaves showed that flavonoid glycosides and bufadienolides are the major classes of secondary metabolites. Fractions enriched in flavonoid glycosides (FEF) and bufadienolides (BEF) were therefore prepared, and their effects on human myometrial contractility were characterised. The repeated addition of FEF, flavonoid aglycon mixture (A-Mix), BEF, or BPJ to the spontaneously contracting human myometrium, led to a progressive decrease of contraction strength, without jeopardising the vitality of the myometrium strips. None of the compounds decreased myometrial cell viability, even at higher concentrations than those used in the myometrium experiments. Results suggest that bufadienolides might be important for the inhibition of myometrium contractility.
Finally, the effects of BPJ compounds on myometrium contractility were studied at the cellular level. The inhibitory effects of BPJ, BEF, FEF, A-Mix, bersaldegenin-1,3,5-orthoacetate (BO), the combination of BEF plus FEF and BEF plus A-Mix on the secondary intracellular effects triggered by OT, such as changes in intracellular calcium levels and phosphorylation of mitogen activated protein kinases (MAPKs) were compared. BPJ led to a concentration-dependent decrease of the OT-induced increase of intracellular calcium concentration ([Ca2+]i) in two myometrium cell lines, achieving ca. 75% inhibition. BEF, FEF, A-Mix, BO, and both combinations led to a concentration-dependent decrease of the OT-induced increase of [Ca2+]i in hTERT-C3 cells. BEF, FEF, BO, and A-Mix, at concentrations corresponding to BPJ, led to a ca. 25% decrease of the OT-induced increase of [Ca2+]i. The combination of BEF plus FEF led to a decrease of 55.3% while BEF plus A-Mix led to a decrease of 38%. In addition, BPJ significantly reduced OT-induced phosphorylation of MAPKs SAPK/JNK and ERK1/2 at its maximum (5 min incubation). Also, at the cellular level, the results suggest that bufadienolides might be mainly responsible for the inhibitory effect.
The insights gained from the intensive inhibition of human myometrium contractility by B. pinnatum are promising and support its use as an add-on medication with therapeutic potential.