Smooth muscle signalling pathways in health and disease

In vitro and in silico studies of 8(17),12E,14-labdatrien-18-oic acid in airways smooth muscle relaxation: new molecular insights about its mechanism of action

In the field of experimental pharmacology, researchers continuously investigate new relaxant agents of the airway smooth muscle cells (ASMCs), since the pathophysiology of respiratory illnesses, such as asthma, involves hyperresponsiveness and changes in ASMC homeostasis. In this scenario, labdane-type diterpenes, like forskolin (FSK), are a class of compounds known for their relaxing action on smooth muscle cells (SMCs), being this phenomenon related to the direct activation of AC-cAMP-PKA pathway. Considering the continuous effort of our group to study the mechanism of action and prospecting for compounds isolated from natural sources, in this paper, we presented how the diterpene 8(17),12E,14-labdatrien-18-oic acid (LBD) promotes relaxant effect on ASMC, performing in vitro experiments using isolated guinea pig trachea and in silico molecular docking/dynamics simulations. In vitro experiments showed that in the presence of aminophylline, FSK and LBD had their relaxant effect potentiated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 1.5 ± 0.3 × 10^-6 M for LBD and from 2.0 ± 0.2 × 10^-7 M to 6.4 ± 0.4 × 10^-8 M for FSK) while in the presence of Rp-cAMPS this effect was attenuated (EC₅₀ from 1.4 ± 0.2 × 10^-5 M to 3 × 10^-4 M for LBD and from 2.0 ± 0.2 × 10^-7 to 3.1 ± 1.0 × 10^-6 M for FSK). Additionally, in silico simulations evidenced that the lipophilic character of LBD is probably responsible for its stability on AC binding site. LBD presented two preferential orientations, where the double bonds of the isoprene moiety as well as the unique polar group (carboxylic acid) in this compound form important anchoring points. In this sense, we consider that the LBD can interact stabilizing the catalytic dimmer of AC as the FSK, although less efficiently.

Effect of drug-containing serum of immature bitter orange on cell contraction, intracellular Ca2+ concentration and calmodulin expression in rat antral smooth muscle cells

AIM: To observe the effect of drug-containing serum of single herb immature bitter orange on cell contraction, intracellular Ca²⁺ concentration and calmodulin expression in rat antral smooth muscle cells.

METHODS: Rat drug-containing serum of immature bitter orange was prepared using the routine method. The drug-containing serum was divided into different concentration groups (10%, 20%, and 50% drug-containing serum), and normal serum was used as a blank control. Antral smooth muscle cells were extracted using enzymatic method and cultured. The effect of each group of serum on antral smooth muscle cell contraction was observed under an inverted microscope. The changes of intracellular Ca²⁺ concentration in the antral smooth muscle cells were tested using confocal laser scanning microscopy. Calmodulin expression in antral smooth muscle cells was detected using immunohistochemical method.

RESULTS: The effect of drug-containing serum of immature bitter orange on antral smooth muscle cell contraction and intracellular Ca²⁺ fluorescence intensity was dose-dependent. Cell contraction and intracellular Ca²⁺ fluorescence intensity increased with the increase of drug concentration (P < 0.05). Antral smooth muscle cell contraction and intracellular Ca²⁺ fluorescence intensity differed significantly between the 20% and 50% drug-containing serum groups and the blank control group (P < 0.05). Antral smooth muscle intracellular calmodulin expression differed significantly between the 50% drug-containing serum group and the blank control group (P < 0.05).

CONCLUSION: The drug-containing serum of immature bitter orange can promote antral smooth muscle cell contraction possibly via mechanism related to the increase of intracellular Ca²⁺ concentration and the modulation of calmodulin expression.