Honokiol blocks store operated calcium entry in CHO cells expressing the M3 muscarinic receptor: honokiol and muscarinic signaling

Abstract

BackgroundHonokiol, a cell-permeable phenolic compound derived from the bark of magnolia trees and present in Asian herbal teas, has a unique array of pharmacological actions, including the inhibition of multiple autonomic responses. We determined the effects of honokiol on calcium signaling underlying transmission mediated by human M3 muscarinic receptors expressed in Chinese hamster ovary (CHO) cells. Receptor binding was determined in radiolabelled ligand binding assays; changes in intracellular calcium concentrations were determined using a fura-2 ratiometric imaging protocol; cytotoxicity was determined using a dye reduction assay.ResultsHonokiol had a potent (EC50 ≈ 5 μmol/l) inhibitory effect on store operated calcium entry (SOCE) that was induced by activation of the M3 receptors. This effect was specific, rapid and partially reversible, and was seen at concentrations not associated with cytotoxicity, inhibition of IP3 receptor-mediated calcium release, depletion of ER calcium stores, or disruption of M3 receptor binding.ConclusionsIt is likely that an inhibition of SOCE contributes to honokiol disruption of parasympathetic motor functions, as well as many of its beneficial pharmacological properties.

Systems Pharmacology Dissection of Multi-Scale Mechanisms of Action of Huo-Xiang-Zheng-Qi Formula for the Treatment of Gastrointestinal Diseases

“…In addition, hydrophobic effects exist between the propyl side chain of HP02 and hydrophobic amino acid. All these interactions ensure the steady state of HP02 in the binding cavity, which well corresponds with the experimental result that HP02 potently inhibits M3 muscarinic receptors (CHRM3) (with EC 50 = 5 μmol/l) and in this way regulates the GI motility (Wang et al, 2013). As for Figure 12B, GC08 (Maackiain) is fixed in the cavity through three H-bonds, including Asp84…O, Tyr85…O, and Ala172…O.…”

Effectiveness in the Block by Honokiol, a Dimerized Allylphenol from Magnolia Officinalis, of Hyperpolarization-Activated Cation Current and Delayed-Rectifier K+ Current

“…Previous studies have demonstrated the effectiveness of HNK in blocking store-operated Ca 2+ entry in CHO cells expressing the M 3 muscarinic receptor, possibly via a mechanism through its binding to muscarinic receptors [ 16 , 55 ]. However, in the present observations, the subsequent addition of atropine (10 μM), still in the continued presence of HNK (10 μM), was found to produce minimal modifications on HNK-mediated inhibition of I h in GH 3 cells.…”

Oxidative stress disruption of receptor-mediated calcium signaling mechanisms

“…In contrast, addition of certain direct SOCE channel inhibitors (e.g., 2-aminoethoxydiphenylborane, zinc oxide nanoparticles [16], and honokiol [21]; see insert to Figure 4) cause immediate reductions in SOCE (Aronstam et al, unpublished observations). This is consistent with the time-dependent effects of tBHP on production of ROS, and suggests that tBHP does not interact directly with the channel protein.…”

“…tBHP (20 mM) was added at the 120 sec time point, as indicated by the arrow labeled “tBHP”. Under these assay conditions, the addition of direct inhibitors of SOCE channels, such as honokiol [21], 2-aminoethoxydiphenylborane, 1-(5-chloronaphthalenesulfonyl)homo piperazine hydrochloride (ML 9), and ZnO nanoparticles, cause an immediate reduction of SOCE; data from a typical experiment with 30 μM honokiol are presented in the insert for comparison purposes.…”